Can I Stop Having my Orthodontist Treatment?

I lost my retainer in a restaurant, and in order to replace the retainer, it will cost my family $500. So instead of having to pay that amount of money, is it possible just to stop my treatment since my teeth have already gone through the braces stage? It's not a big deal if my teeth shift, and it would a lot if we don't have to pay $500 dollars for pieces of plastic made to keep my teeth straight. I don't mean it in a bad way, but is it a big deal if I stop?