I saw in the eBay auction ad, that the leak was in a welded seam.
Is it a rust through the seam, or has the weld just separated ?
Another member here ,Thrang, just did some resealing of a rusted tank on an asian bike that his wife rides. Didn't sound like it was very costly to do it.
I think the chances of getting any where near a match on the paint is going to be minimal with spray type rattle cans.