I love that year paint scheme. There are shops that use little tools to tap out dents in cars from the inside, but the tank is probably thicker metal than a car fender so they may not be able to help. Worth asking though I would think.
If you find a tank in that color in better condition, you can help offset the cost by posting yours on eBay or something. It's functional, even with the dent and some folks would find your tank a step up from theirs if they have rust or even larger dents.
One thing you might consider is hiding the dent with some sort of saddle bag style holder. I've seem 'em for quads and also some that hold a pair of water bottles. They go around the gas cap and hang even down both sides of the tank to carry stuff. At least for the time being, it would hide the dent and you might find it so useful that you decide the dent isn't worth bothering with after.