Hey you guys, thanks for all the advice!

Well, I had done some research online on craigslist, classifieds and websites of used-bike shops and found that used (non x-mart) bikes also sell in the $200+ range which is why I had decided to get a new entry level Specialized.
So I have three questions:

1. Isn't it worth it if you buy a good lock (which will deter bike thieves), and then, in the event that the bike does get stolen, you claim the warranty from the lock manufacturer?
2. Why are even used bikes so expensive, or am I not looking in the right places? i.e, how much should i pay for a good 'beater'?
3. Is a new x-mart bike better than a used 'beater' for the same price?

Then again, I haven't done any ground work and have just found all info online. I need to visit the local bike shops, once I get freed from midterms!