Build one using the old desk as a start, get new legs from somewhere like Ikea (cheap) and a new top for the other side of the L, could probably do it for as little as $50 (guessing here, I live in the UK not US )

edit: or ebay a desk, noticed they go cheap on ebay as they're hard to ship, but try and find one to collect and ur sorted, that or a local paper or something with 2nd hand desks?