Cheeseplantmad
I think £5 for half hours watering plants is fair , it’s not a difficult job is it , my grown up gardener only charges £12 hour and he does considerably more than that . But , I’d prefer to look into buying some “ self watering “ kits for when away on holidays , there are many ideas online for self - watering plants , that way you can be totally independent .
I'd look for a self-watering system too.
Our neighbours water our plants when we're away and we'd do the same for them.
We buy them a present and they do the same.