This just cam on ebay. A 1989 fuel tank. Looks like they're parting the bike as I also saw the matching tail pieces.
http://cgi.ebay.com/ebaymotors/SUZUKI-89-GS500-GS-500E-GS-500-GAS-TANK-_W0QQcmdZViewItemQQhashZitem35aebe4705QQitemZ230564972293QQptZMotorcyclesQ5fPartsQ5fAccessories
WOW... is that a normal price for the older tank??? I've got one that I need to swap for a newer tank.
That is a used tank. New ones, when you can find them, are around $500. I have one but no one wants it.