Most radiator shops offer gas tank boilout in their famous caustic tanks. It's usually a fixed price including a liner product which seals pinhole corrosion and is alchohol/benzene resistant. Between 70-100 $ sounds about right. I have wired my filler tube to the tank so it would get the same treatment. Short of buying a new tank, this is a good investment. The shop deals with the hazardous residues and leaves a nicely hot tanked, sealed tank.
While you are at it, new fuel lines and hoses will complete the job. I don't mess with the home cleaning anymore since the local shop does a much better job. Whatcom Radiator in Bellingham is who I use. They have done five tanks for me through the last few years.
