Remarked,
I think that one of the most important things that you can do is "quanitify" everything with the person doing the work. Along with quantity, I would add value to each item. Another way to put it would be to itemize the bid. Don't take the "we'll do it all for x amount of dollars...." routine. You need to know exactly what you are getting for your money, and another key is to make them do what they say, or they don't get paid.
If you decided to go T&M, you could set up a reasonable budget for material, and then try to determine a range of time that the job could be completed in. With that in mind you could set a "price not to exceed".
I wish I could give you more, and better advice, but without being there, I can't. Just remember:
1. Determine the scope of work
2. Quantity
3. Price each item
4. Make them up hold their end of the deal
5. If they don't, then they don't get paid
I wish you the best,
Doc
