Another plane to consider is the World Model Sky Raider Mk II. Powered with a Super Tiger GS-40w/Macs muffler it was very aerobatic with good vertical performance, and many people race them with ball bearing .46 engines (I like the .46 AX w/Macs muffler) and they can be quite fast. While Macs mufflers aren't cheap - about $36.00 at tower - they don't come apart in flight, are a bit lighter and work almost like a mini-tuned pipe. Speed wise they top out about 85 mph or so.

For earning aerobatics, sport aerobatics, and general sport flying they really do well and will do just about any maneuver a sport plane can do including sustained knife edge and great slow rolls without losing altitude. Plus they slow down as slow as a trainer for landing (I like to hold full up elevator and fly a very steep decent right at the edge of a stall controlled with power only and add just a touch of power for a round-out and soft touchdown). On the slow end, they are extremely stable don't drop a wing in a mild stall. On the ground I have yet to be able to ground loop one, and I've intentionally tried - it just won't swing around!

You should be able to get a Sky Raider for under $100.

Hogflyer