Hmm i reckon SMA at tempe will be the easiest one i know to get to if you are looking at electric racing.

With regards to classes the cheapest class probably to race is 540 if you already have a suitable car. Otherwise if you are starting to race mini's may be a little cheaper to get going but not all clubs have a big mini following (if one at all). SMA does run quite a few minis.

I dont want to scare you off but to be ultra competitive these days you do have to spend some money to get extra power out of your car though

If you are looking to get into racing you should head down to the club and have a chat with the people so they can tell you what to buy and where the best places to buy them from are. SMA ( http://www.smaracing.org/content/ ) is based around the Jets Sports Club so if you head down there you can always sit down have a beer or two and a good feed from the bistro while taking a look.