Company founder decided to not pay me for work done and has come up with "reasons" for it. What recourse is available without a lawsuit? I am going to guess, it is probably none, but might be good to ask HN.
Or would HN recommend that I sell my work as a SaaS product?
Your work has no value without customers, though. You won't be able to just deploy it as a SaaS and watch the money roll in.
If you had a contract, take him to small claims court. It should be a slam dunk. Otherwise write it off and remember to have a good contract in the future (and maybe even escrow).