If you install car alarms like I do, it's not going to worth your trouble to install it. Routing wires, wrapping wires, hiding everything, takes way too much time. But if you don't care for the stealthy-ness and a clean job. It shouldn't take long.
I am by no means a pro installer, I just do my own stuff so don't quote me entirely on it. But if you only care for lock and unlock, it's be a few wires (ground, constant 12v, lock/unlock, siren (stock horn you'll need to use a relay), more or less). To install the whole alarm, you could probably get away with using like 10ish wires from the alarm system. And if you don't care for it being super clean, you could just use these "Y" splicing things so you don't have to cut as many wires.
Also you can sometimes find people on craigslist that'll install alarms for like 80 bucks (in my area at least). I just like saving money, 80 dollars for them to do it in 2 hours or 80 for me to do it in 8... 10 bucks an hour is more than minimum wage! I'll do it myself.
I'm sure my input has helped you just as much if I didn't post. But i went too far typing so I just continued.