I dont know of really any to avoid. That depends on what you want i guess. Have you ever heard of Audio review.com? You can go read through reviews there. That should give you some idea. as long as you can sort through the real reviews and the bs ones. For the price your looking at i suggest you check out the diy kit sub from parts express. Its $350 and no doubt it will demolish the competiton.(except my new faverite speaker company AXIOM of course)
Heres a link to the parts express sub..
http://www.partsexpress.com/pe/pshowdetl.cfm?&PartNumber=300-739&DID=7
