Well then it would kinda depend on the size track you would run on. If you are just getting into racing there are plenty of good choices that can be had for around $200.

If you are on a fairly small track then i wouldnt overlook the werks b2 also. Im hearing its a lot of engine for the $160-$170 price tag.

Do some reading and find out what you might need. Some engines deliver more rpm and horsepower, and others make a lot of torque. Some give a nice smooth mix of both. Dont overlook any kind of pipe you may need to match well to the engine. Some pipes sound like they mesh well with other brands, while some do not.

Get familiar with what you read and check out some videos! Research helps a ton with making a good choice! I would much rather suggest a good engine for the money and get a matching pipe and a good clutch kit, vs dropping $400 on an engine alone.

Might be a good idea to head to your local track and ask some questions.