what home alarm system is most reliable and affordable?

Go to http://www.x10.com - They have several wireless home systems that work very well and don't cost a lot. Installation is easy. One system even has an autodialer that you can program to call several different phone numbers (YOUR phone numbers, don't progam it to call the police or you could be in serious trouble, doing that requires permits!).
Voxcom, Alarmforce, etcc There all pretty good and usually $20-$25 a month.