Glenn it's not hard to do a good job, just take your time and be careful. Those places charge heaps for installations, and in my opinion not worth it. What are they gonna do, wire it all up, do a simple amp mounting and a basic sealed box? It's all terribly easy shit. You heard my system, and that was 100% installed by me. Everything. Only the box for the 12s I didn't build, but that will be replaced soon with one built by me, and it will be heaps better than it currently is.
Seriously, you can learn heaps from it all and when you show it off to people you can also show off the fact that you did it all yourself, and be proud. I know I am, and the same would go for Bass Crazy and SPHELL and everyone else has done it themselves.