From memory that's not a bad price. I think I got quoted tanks starting at $200ish up to $400 for a fairly good, straight tank. The old memory isn't what it used to be, so don't quote me on that

The price depended on if the tank had any dints in it, and the amount of rust inside it

I think that was through Sumoto. Your friend should give them a call and find out, then try and get it from somewhere else. He might be able to get a reasonable one from a wreckers fairly cheap, but he might have to repaint it. I would say most of them have rust in the tank too, as these bikes have been sitting in the weather in some storage yard in japan for quite a few years. A cheap fix for that though is to get the DIY polyurethane liner kit. Costs about $80 and lines the inside of the tank with plastic. I've got the kit for my ZXR250, but I haven't done it yet, so I can't tell you how difficult it is to do. HTH
Most motorcycle problems are caused by the nut that connects the handlebars to the saddle.