Check out the FMF bikes available from the danscomp.com site. They are good, affordable BMX racers that will serve you well in the short term. Eventually, to be truly competitive you'll need to build a serious race bike, but that is a huge leap up in price (not too different from the old days, huh?). Remember to reinforce the fun aspect of racing first. A kid shouldn't expect to podium first time out, especially against other kids with more experience. Same for you. Enter whatever class they want you to enter in, gate like old times and crank like mad, go for the double and smile having fun even if you're dead last.

Also, check out the Redlines (my personal favorites) as they are still top shelf bikes, unlike most of the other brands from the heyday. SE bikes are making a comeback as well, as is Kuwahara. Basically, a good $300 bike isn't going to break the bank, should be relatively competitive, upgradable and if you decide racing just isn't in your blood anymore, they make fun bikes to tool around the neighborhood on.

-Paul