I would agree with BBD on that. Check local papers, music stores, and eBay for used instruments. If you find a nice used Fender Precision or Fender Jazz in the $500 range, go for it. But you need to make certain you can tell whether the Fender is passive or active (costs more, usually has"Deluxe" in the name). You can usually find a 4 or 5 string Peavey Cirrus in the $600 - 700 range. These basses are grossly under-rated. It would be worth waiting and saving up an additional couple hundred. If you have a Cirrus, you really wouldn't need another bass.
Peace,
James