So help me out. I need a PC with at least one PCI-e slot, that is spec'ed out to run a double handful of plug ins, and hopefully be reasonably priced. I know I can spend 1500+ and get good results, but I'm going to pay for all of this by selling my current Impact servers with Yamaha cards. A PC closer to 500 bucks would be a lot better.
So how much PC do I really need for this?
I am not sure if you mentioned building, if so I would not recommend that, home brewed machines are not the most stable.
For machines I would recommend checking out Dell Outlet. They run pretty good discounts all the time, and roughly once a month they have an additional big sale (get on the email list). Specifically check out the commercial series stuff. About a year ago I bought $2k laptop for about $900ish once I added all the coupons together. It can run over a 100 plugins at 4% processor capacity. Sure not the Dell stuff I grew up with! Get us much computer as you can afford.
Keep in mind I usually use an Extreme C Server when live, just for the sake of safety, but if not live I don't usually bother getting the server out.