how long after buying a used cheap car can we file for bankruptcy? we would still want to pay that agreement.

Why would you need to wait at all?  There are numerous factors that go into determining which bankruptcy chapter to file under and when to file.  You need to have a consultation with a bankruptcy attorney in your area to evaluate your options and answer your questions. Be sure your attorney is thorough in their consultation. Mark Markus has been practicing exclusively bankruptcy law in California since 1991.  He is a Certified Specialist in Bankruptcy Law by the State Bar of California Board of Legal Specialization,  AV-Rated by martindale.com, and A+ rated by the Better Business Bureau.