Depending on where you live, there should be plenty of alarm companies. Find a smaller one that is local, call them up and talk to them telling them how you feel. They want to make money and want customers. The reason they want contracts is so they can guarantee a cash flow and subsidize the free system, free installation or whatever the case may be. Obviously to buy one will cost money, and to have someone install it will cost money. It's like buying an unlocked cell phone, or a cell phone out of contract. It isn't subsidized by that 2-year contract you sign, and will most likely be full price with a small mark-up.
So, if you call them up, explain it, have them come put in a basic system, the installation should cost, depending on a lot, $100-$200. The system itself will cost $300-$400 depending on their mark-up. So you are looking at about $400-$600 to have them install it and make it worth their basic time.
As for monitoring, there are places on the web that charge $10 or so for monitoring. Not sure I would place my hope in them. I have worked with Monitronics in the past and would trust them. But that is all up to you. If it is Monitronics, there are many dealerships and you can secure pretty cheap monitoring, especially since you would have a system already installed. If you bargain with them, you can get it down. Getting set up on a month to month contract is possible, they pay $5-$6 per month to have it monitored by Monitronics, and charge whatever they want. Obviously they are going to want to have you locked in, but if you find a nice one and explain to them your situation, it should work.
One thing I might add, if you aren't under contract, the chance of you getting a free warranty on your system is going to be difficult, at least with Monitronics. The company wants to make it worth their time, and to them, that is signing people up on contracts.
Realize that going into it. Also, if you are worried about them messing up during the contract, make sure you get all your worries worked out, then sign the contract, it may save.
Do what is best for you, not them though.
3 years experience in alarms and past dealership owner.