That's more of a subjective matter which depends on the dynamics of the relationships.
So thus far they've been happy to pitch in for no compensation? It sounds like then you need some 'pay rate' that (a) will keep you from feeling like you're taking ongoing advantage of their friendships; (b) will similarly prevent them from thinking that you're making an undue imposition on their kindness; and (c) isn't so large that it makes it no longer worth your while to keep running the biz.
While (c) can easily be reduced to a calculation, (a) and (b) are subjective calls that depend on the nature of the relationships, the situation, and the people involved.
As a start, though, you might place a few phone calls around to see what's the going rate in your area for people who are doing similar work.
Couple of tangent thoughts, though, that you'll want to keep in mind (although not directly addressing your question). For one, you mentioned that some of your worker bees are doing some driving (deliveries, I suppose?). If they're using their own vehicles, you'll want to add a mileage or gas reimbursement to their hourly pay.
Also, whenever you're paying for personal services in a business, there are some employee / independent contractor issues that unavoidably become involved. Tax withholdings, W-2s or 1099s, some paperwork, etc. That's another topic, and you should bounce it off of an accountant who's got the expertise in this arena.
Best success wishes for your biz (great name, BTW!) Cheers!
...it was early and I was full of no coffee...