Demaestro - 7:06 pm on Oct 6, 2010 (gmt 0)
Make up a contract. Without it you have no protection.
As far as appraisals it is hard to come up with a value when you have no income from it.
What is it worth to you? Could you move the site to a new domain?
What is it worth to him? How long would it take him to achieve your rankings?
Then most importantly... what is his budget?
Once you know these things you can come to a decision on what it is worth.
Then factor in, will you get paid work from this? If yes perhaps it is worth coming down in price if you are out of his budget.
I wouldn't waste money on an appraisal.