I'm unable to walk my dogs, too, due to having both M.E. and Long Covid together - as said above, circumstances change! (I do hate judgemental morons who go off blowing their trumpet whilst knowing F-all about the background. My goat has just been got, lol)
I can't help you regarding cost, as that will vary dependent on the area; the number of dogs to be walked; how long you want them walked for and whether or not you give or refuse permission for them to be walked with other unknown dogs. (I would defo not want that.)
What I definitely advise is that you only use a Walker who has comprehensive insurance, covering vet bills for your dogs if injured AND any creature/human your dogs might injure - however inadvertently - plus any property damage your dogs are blamed for, including slipping a collar and causing a traffic accident.
Also make sure that if the Walker is going to drive your dogs anywhere for their walk, s/he has permission in print from the car insurance company they use to do so. If they don't declare the Walking as a paid occupation and proceed to have an accident with your dogs in their car, it invalidates their insurance.
Re finding a properly insured Walker, have a look over this: tinyurl.com/4ff73yhv
Also, you may be able to find a resource like the one I use: a fully dog-proofed meadow with poo bags and bins; running water - only for dogs to drink, as washing 'em down would create mud everywhere - a small agility course and a water/wind proof hut with seats for poorly or just tired owners. You'd need someone with you capable of keeping watch over the dogs so's they could poop-scoop, of course.
Here's a link to mine just to give you an idea of how it goes. (It's incredibly reasonable priced too: £6 per half hour slot for up to 4 dogs, £7 ditto for over 4.)
www.poundingpawz.co.uk/
This has turned into a book, rather than a post so I'll get off now - wishing you luck in finding just the right person.