Get an RB C5 .21, you should be able to find one under $450.00. I just bought a new one for $350.00 off of ebay. Here's why I'm sold on RB as being the most reliable;
I bought a Brand NEW RB C5 Rody in June of 2002 off EBAY for $420.00, I ran it the last half of that season. Then in 2003 I raced it from March until October, and depending on the weather, I raced it 2 to 4 times a month running 30% and 40% nitro in it. In between the 2002 and 2003 season I had the piston and sleeve re-newed and changed the conrod in it.
I ran 17 gallons of fuel through it before the conrod finally blew. I routinely cleaned and re-lubed it after every 2 race weekends. I never had a problem with it starting up on the first or second bump.
You may not be able to find a C5 Rody for under $450.00, but I'm sure you can get a C5 under that price. The powerband on the RBs is very nice. Perfect power for the tracks we have around here, S&J, OTH, Fastlane, Richmond Va. The JPs, Nova MAX, and other extreme high end engines are overkill.
You'll be very happy with the C5, just add a .1mm head shim, run 30% and you'll be very happy. S&J hobbies has one for sell right now, it may be in your price range.