The Fed cut the interest rate 3/4 of a point today so you may be able to do a little better on the loan now.
You're getting some great advice here. OT is right on - they have ways to negate future payments. Ask Queenie. She just went back to court several years later to get her X to pay something he agreed to and she really doesn't know if or when she'll get it.
I laughed when I read your STBX got value from the internet. I'm not a residential appraiser but I could be if I wanted to. It's just too hard to switch from commercial to residential - the learning curve is great. Anyway, glad you got him to agree. Just be certain your numbers are good ones. We're not usually very business-like when we think of our homes. And with the way the housing market is now, I'd be careful.