You should have been able to get a new one at the gun show for about $75.00 more. IMHO you are better off with new if you can swing it. Some of these guys at guns shows can be a little on the shady side and you just never know.

Baldy seems to be correct on the price for the basic gun, but the extra magazine(s) do add some value. A spare factory magazine for the P90 costs between $30 and $40; the extra-long mags made by other companies are probably worth less. Even so, the extra mags probably add about $40-$50 to the value of the package deal on the used gun (I think new P90s only come with two mags), so you need to take that into consideration.

I still think the price was a bit high for a blued gun, but handgun prices can vary quite a bit from region to region. I've seen used blue-finish P90s pretty regularly in my local area for around $300 or less, and I paid about $250 for mine which has some dents and finish wear on the frame and slide. Stainless steel P90s (technically called KP90s) are higher priced, and if the one you looked at was stainless, then with the spare mags the price wasn't too far out-of-line, in my opinion.

Thanks for the input and it was the stainless model.