Frostpaw, I would encourage you to get dual subs for the best results, and also experiment with subwoofer placement. Multiple subs systems have some very serious advantages over single sub systems, even if the multiple subs aren't quite as good as the single sub. If you ask about it in the subwoofer forum, you will fine a lot of agreement on that point.
As for the kits, you might not be great at woodworking, but there may be cabinet makers around you who can put the cabinets together for not too much money. It's worth making a couple phone calls and asking about anyway, considering the massive bang for the buck you can get with those kits.
Anyway, if that is a no-go, some other options I would consider in your budget are the QSC K10
s. These are very highly regarded PA speakers that some have used in their home theaters with great success. That will get you some real THX Reference levels as well. Pdxrealtor, you might consider those over the Klipsch as well, since you are using an AT screen, they will be a lot more powerful than the Klipsch, and are purported to have very good sound quality. If you guys have a Guitar Center or some other pro-audio store around you, I would call them up and ask for a demo at the very least.
While you are at the pro-audio store, you might check out the Rokit 10-3 monitors
. I think they would work well in a home theater application as well. They won't be as powerful as the K10s, but they are some relatively powerful monitors that will give you a very neutral, linear sound.
What's great about the K10s and Rokits is they are self-powered and so won't put any strain on your amplifier, which helps it last a lot longer. Active speakers are usually a lot more efficient with their power as well. Of course, you will want a receiver with some good pre-outs for these.