Because of the extention I would say reg fee to low $xx
I own some of the hyphened two letter domains and in my opinion the hyphen isn't that bad at all. Taking in mind you can't reg any two letter domains and if one comes available you'll need a jackpot in order to be able to pay for them.
Not long ago si.net was sold for little over $11k on Snapnames.
When the regular .com or .net two letter domain isn't available or not developed than the hyphened one is a very nice option to go for. Saves you alot of money, will cost you a few visitors that has to be said but all in all you'll come out as a winner I'm sure.
Nevertheless goodluck with (re)selling/developing your names.
Cheers