Magnum,
Its not my top option for carry, but I too have a P90, which I absolutely adore and mention about every post I make on THR, and I have carried it successfully. One modification that I highly recommend is that if it does not have the Hogue wrap-around grips on it, spend another 15-20 bucks and make that change. Grips are obviously a pretty personal issue, but I would say 95% of the people that have shot my P90 prefer the wrap-arounds over the flat polymer panels. Personally, those grips totally changed my mind on the P90. Prior to those grips, I was having a real problem shooting my pistol accurately. Adding those grips had the effect of forcing my hand into the proper position, in addition to being substantially "tackier" than the hard plastic panels were, and my accuracy soared. They are also just a lot more comfortable to hold onto. Anyway, thats just my 2% of a dollar, but if your expereince with your Ruger is anything like mine, I think that you will be exceptionally happy with your purchase. By the way, thats not the cheapest I have ever seen a used p89 go for (cheapest was 125.00 from a guy selling ALL of his guns. I could only afford one, so I picked up a MkII from him for 100.00 even), but that is a very, very good price, and I think you got a heck of a deal.
Timbo