I agree that the house should be professionally appraised. It really doesn't cost that much in the big scheme of things, and it's good to have an objective outside opinion.
If you can gather information on what comps in the area have sold for, that may be helpful too.
Property tax assessments are not a valid way to appraise the house value.
THEN - run these calculations by your H. (Note that this is NOT the way it is usually done, but SHOULD be, as it is the fairest way to value things):
Imagine that you have a house with market value of 200k, and a mortgage of 100k, so you have 100k in equity.
The typical calculation would be for you to pay him 50k to buy out his half.
HOWEVER, if you SOLD the house, you would NOT gain 100k profit. You would have to subtract from that realtor fees, advertising costs, and the cost of repairs and fixing up the house to sell. Since realtor fees are typically 6%, plus you might easily have 1,000 to 5,000 dollars worth of repair costs, figure you spend 15k on those items - leaving only 85k profit. In that case, ex only gets 42,500, NOT 50,000.
