im currently in the process of installing an alarm in my own car. i figured it'd be an easy job, because like you, i have also done audio installs before hand. an alarm installation is totally different. so many wires, and if you don't know which wires to tap or where to find those wires, you can find yourself in a lot of hot water. i havent found a wiring diagram that was absolutely correct, and i've had to find my wires through trial and error. i can understand why shops would charge so much for installation, and had i known what i was getting into, i would have gladly paid it. if you can find a good guide (wire colors and location and everything) it might be worth a shot. i'm going blind right now and after a week of working on it, im just now finishing up the last few wires.

the directions the car alarm manual gives you are a joke.
as for car alarm brands... clifford, dei, and compustar seem to be pretty well regarded here on the board. just find a brand that has the features you want.
i hope this helps a little at least.