I would buy a new CO2 regulator and then use my old one on my nano. Or, I would find a high quality 20L that is rimless, which I have seen for $80ish, spend the rest on aquasoil. Third option, keep what I got an get a 5ish gallon cube. I think I could do the full setup for $200, especially since I have an extra canister.
Honestly, at this point, I really don't need anything, some components could be improved upon.