Probably $450 or so. Lots of variables to deal with. Might be somewhat
less than that if you try to sell it quickly.
One of the problems you might run into is that a lot of gun shops seem to
have an abundant supply of used Walther P99 .40s, and a lot of people seem to
perceive the P99 as being "better" than the SW99 is, rightly or wrongly. So
in terms of selling it, you'll have to deal with that.
I know most of you will think I'm nuts, but as I like 9mm and .45, and I can't get the 1911 I want yet either, so this makes sense to me. I have big hands and fat fingers.