Current scrap value is probably around what you have in the machine. It might even be slightly more depending on where you"re at. I believe that"s about a 15,000 lb machine, so call up your local scrap dealers and see what they"ll give you. You're better off paying more and starting off with a better machine.
You should learn as much as you can and also have a knowledgeable person come with you when you check out any prospective machines. Expect to pay at least $5K or more for a 450 size machine in good condition with a good U/C.
But before buying anything, analyze what your needs are and decide if you really need a crawler or if hiring out a pro is your best bet. For most people, hiring the job out is the best bet.