You have certainly started off on the right foot. I bought my NA on impulse. I have not been disappoi9nted in it, however I found this forum afterward and would have benefitted had I done things in reverse as you are. If you are serious about the SRT-6, as you seem to be, there are currently 60 for sale on AutoTrader. If you $15K limit is based on cash, you have an excellent buying tool. If it's based on monthly payments, dicker with the interest rates, and length of loan. Perhaps you can move up a notch with longer loan.
Have you ever searched Autotrader? If so you should be able to find what you want. If not, PM me and I will walk you through the steps so you can cut out the items you don't want.

John P
AKA FTroopChief