If you are a drinking man, I recommend an evening's worth of your favorite beverage. (My favorite beverage is a good IPA, followed by a good single malt Scotch, or a single barrel bourbon, being a Kentuckian of Scottish ancestry, that is what I want).
If you don't drink, a 6pack of Torpedo IPA costs about $10 in my area. Co-incidentally, this is just above minimum wage for an hour's work. I don't approve of minimum wage legislation, but I certainly don't think my labor is worth less than minimum wage.
Doing simple tasks for technically inept people is fine, a good way to make friends. I do believe that they should pay some thing, though. If disguised, (as beer), or some thing else, (insert other cost here), it is fine.
Really good friends do things for each other all of the time, so no accounting required there.