what is making it non-functional? sensors not working? keypad broken? rats at the low voltage wiring? panel fried? I think if the wiring is all good you can reuse that and replace whatever hardware i would imagine???
or you can go with wireless security system...i just did a simple google search and this came up on amazon that seems to have good reviews
Amazon.com: Simplisafe2 Wireless Home Security System 8-piece Plus Package: Home Improvement