The patch would be easy and cheap, it's the respray that's the expensive part for sure. It's just enough that the weld is going to burn into a visible area, so you really would have to repaint that whole panel. Luckily it's not on the roof part or something.

All I have access to most of the time is a flux welder, and I've done way more delicate repairs than that. You might practice a bit and try it yourself. You'll have to do a good job of protecting the surrounding area from spatter, especially the interior. Flux spatter will even melt into glass if it hits it. Lastly, Forney is the cleanest flux wire brand I've ever used so you might look for some of that to give yourself a leg up.

Otherwise I've seen many POR-15/Miracle Paint and fiberglass repairs that were permanent so for an inconspicuous area like that I wouldn't have a problem with it. It'll certainly never rust again.

Finally, you can get all the factory colors in a spray from Paintscratch.com and they look great, especially if you opt for the 2k clear in a spray can. So that would keep it all under $100 if you did everything yourself.

-Rog