What is the minimum amount you can sue in civil court?

$20

It depends on the jurisdiction in question. Nowadays, most claims under $10,000 are legally required to be handled in Small Claims Court. The minimum you can ask for is generally an artifact of old legislation in your area, and may be set ridiculously low (as the above $20 indicates), or may have been updated more recently to something reasonable (like $100 or more). Ask your local Sheriff or city Police Department (or, District Attorney's office), as they should know for sure in your area.