Thanks again for the response. I did some online research, and it seems the best affordable option was Rustoleum rattle can paint. It's not gasoline-proof, but apparently it's resistant enough that I shouldn't have any problems as long as I don't let it soak in gasoline. The ACE hardware didn't have satin black, so I just went with gloss black.
I also masked the recessed portion around the filler hole before spraying on the top coat, since gasoline is likely to accumulate and pool there after filling up. Shouldn't be a problem, since the filler cap covers that portion of the exposed RustSeal.
I have one question though: how do I know if the Gold Standard Sealer I applied in the tank has adhered well? The design of my tank made it impossible to drain out all the sealer, so I just tried to move the tank around to spread around the excess as much as possible. Even so, parts of the interior of the tank that I can see where the excess sealer ended up shows some minor bubbling. I'm worried about this, so perhaps some advice as to how much bubbling is acceptable? It feels rock hard when I tried to scratch it with my fingernail.