Budget for four week trip to Australia/New Zealand

We have just been on a 3week trip to aus. In total it must have cost about £5k but we stayed with our daughter for 10days so that cut the cost.
There are some very good deals if you would like to hire a motor home in NZ.
My advice is to go Trailfinders with your wish list and see what they can do. We stopped off in Singapore and HK on the way there and back. You may like a round the world ticket. There are so many options to choose from -your perfect holiday is unlikely to be the same as ours.

We recently had a 6 week holiday in Australia, staying with DS and DIL. We had the first night in Sydney and it appeared that all the hotels were charging pretty much the same as each other. We finally found a special offer but it still cost us £186 for one night! When we first visited, 10 years ago, it cost £90 per night which we thought was quite reasonable. Do not underestimate the cost of eating, either. It seemed every pasta lunch cost about £50, dinner was about £100 for 2. We reckoned our holiday cost almost £10K and we were staying with DS! Don't think we'll be doing that again.

Did our retirement trip last year- after a cruise we disembarked in Sydney where we hired a large camper van and drove along the coast to Adelaide-via Melbourne. Booked our stops along the way while still at home so we knew our route, quick trip to Alice Springs and Uluru- fabulous. Then flew to Christchurch NZ, where we hired a car for 2 weeks, again booking small homesteads/ b&b along the way
We used Freedom Australia to book campervan, flights etc so we knew basic costs- on top was fuel, food etc, used bbqs in the campsitesto cook- met lots of lovely people along the way
Probably spent about £12000 in all but we were away a long time. It was an amazing experience, we won’t be going that way again, and we are only on this earth for a short time and wanted to make the most of our time down under

Look on Wotif for offers on hotels if you're doing your own thing, but do check the map to make sure you're near where you want to be.
Sydney is expensive but there are places to eat which could be more reasonable than £100 for two (I think Darling Harbour restaurants are a bit more reasonable).

If you book with one of the travel agents, eg Trailfinders, you may find two internal flights in with the price of the international flight.

Watch the exchange rate too - it's 1.78 dollars to £ today but we've known it fluctuate over the years from about 2.5 down to 1.4, which, of course, makes a difference to your spending money.
Pay in local currency if paying by card; there may be offers to pay in GBP but the rate could be disadvantageous to you then.

I found the Food Halls offer the best deals for eating out. Different stalls clustered round a central table area. There’s a great one in Darwin and a good one in Melbourne too if you want to eat in the centre.
Like everywhere in the world though, eating is cheaper if you travel out of the city centre.

It was more expensive than I’d anticipated.

You don’t say how much of Australia you want to see, internal flights, accommodation, motor home? How long is a piece of string......

We spent a month in New Zealand and did it very much on the cheap. We hired a clapped out old car that drove like a dream and wasn't likely to be targeted by car thieves and we stayed in some brilliant hostels and enjoyed mixing with the young international travellers. We also paid a very reasonable sum to stay in a flat for a week, which we found through airbandb. I'm afraid I can't say exactly how much we spent, but it was no more expensive than our usual holiday costs and I did a lot of research beforehand to get the best deals in accommodation and car hire.

Depends on when you go and which area. You need to check out the climate, the north is wet and dry I wouldn't advice this.

We have been there a couple of times 3 months travelling the east coast which is the basic tourist route in a camper van. This is by far the easiest route for tourists.
You can easily take trains or buses and can buy flexible tickets which allows you to stop off at places of interest.Check out the trains below.
www.seat61.com/Australia.htm

Decide which area you want to see.

There are domestic flights but these can take hours dependant where you are flying from and to.

More recently we travelled the west coast in a camper van from Margaret River (very European with vineyards) to Exmouth (hot as a oven). This takes in Perth which is a wonderful city to visit. There are no trains only buses which run infrequently the further north you go.
The higher up the west coast you go the towns are miles apart, if you have a vehicle you need to take petrol(few petrol stations ) and water. I wouldn't advice this route.

NZ two islands with a ferry between.

We hired a car on each island check out below for trains
www.seat61.com/NewZealand.htm

Accommodation for both countries.
Book on the Internet checking out the reviews it's the easiest way, don't exclude hostels.
You could book a camper van over the Internet we did, which means you have your accommodation.
But don't forget on top of the hire cost there's insurance and fuel, some limit mileage or charge more over certain miles. There can be a charge for more than one driver and there is a minimum/maximum age with most companies.

Best of luck you'll have an amazing visit, I celebrated my 70th birthday in Margaret River and danced for two days solid at a great pub.

Depends on when you go and which area. You need to check out the climate, the north is wet and dry I wouldn't advice this.
If you mean the north-east of Australia Jeanie, then I agree that it would be best to visit in our summer (their winter) as N Queensland's weather is lovely then. If visiting in their summer beware of the possibility (not certainty) of cyclones and it could be very hot and humid.
However, the south of NZ could be rather chilly then.

by 'then' I mean our summer, their winter of course.

I was thinking of Northern Australia round the Darwin area.
10 days is such a short time to spend in this huge wonderful country so it is crucial the lady gets it right where they will visit.
We all have our likes and dislikes what makes the best trip for us is a big consideration and weather can make the difference between a good trip and a great trip.

Thank you all for the very helpful tips. I posted my question a long time ago, but life has got in the way a bit since. However, we are now back on track for a trip in Jan/Feb, spending most of the time in NZ and just stopping off with family in Melbourne for a few days on the way back.