If the buyer is only coming up with 10k, for example, for the first year lease payment in advance, or worse yet, you agree to monthly payments, then I wouldn't even suggest you put the domain into escrow, as you seem to be considering as an alternative to a lawyer and contract. You don't want to put a six figure asset into escrow limbo when the other side is putting up a small percentage of its value for months if not years of control.
I think you are best served by paying an attorney with experience in domain matters putting together their "seller" version of their form contract, most attorneys have two versions of every contract geared to protect their client as either the seller or buyer. You wouldn't want a lawyer who isn't smart enough to have both versions. I believe there are some attorneys that advertise domain transaction expertise in the forum, but I am not familiar with them, unfortunately the copyright attorneys that I have used in the past would be simply too expensive, they would want a 10k retainer to start anything. I would suggest you call a few attorneys, explain the situation, and see if you can get them to prepare a contract for you for a grand or two. Promises for the future mean very little, if you are receiving 10k up front, it is a 10k deal, spend based on that basis as long as you are not actually transferring registration of the domain to anyone other than yourself.
If the buyer insists on escrow, I would take the position it is the same as transfer, and in that case I would suggest that the buyer simply acquire financing.
Congratulations on the sale.
