since you got few responses I will add my 2 cents but I am not overly qualified to comment. My cabinet finisher/refinisher does the local corp. offices of a large company. He will go in 1-2 times a yr on a Saturday and touch up elevators, desks, trim..... He sometimes takes his wife to help and he treats it as extra pocket money. Think it only takes 4-6 hrs He will charge $500-700 each time but that might not be realistic in your situation. Depending on your situation I would love to get 45-75 hr incl. drive time, plus travel expenses. hotel and food expenses. I also would be careful giving an estimate as these things could easily snowball and then there would be hard feelings if it turned into a longer job than you thought. Although I do not do much work out of town a recent job out of town took probably twice as long as I had privately guessed. Luckily I had never visited the job and I billed time and material to the person who contracted it.
Having said that, this past summer I was slow and took on some sub work and only averaged $25 and $45 per hr for some cabinet install and tile work that was priced per unit so the price was set. I did not like it but it was better than earning nothing. Some might say they would not get out of bed for that but I think its good to keep busy and this fall I have plenty of profitable work again.
If you have a good relationship with the builder you might talk to him and try to come up w/ a pricing plan. If he respects your work he will want to pay fairly and your goodwill in helping him may lead to more work although I would not count on that in your pricing. hope this helps, mike