If it looked like the one below, it would be worth what he is asking.
I don't know why they have a reputation for being fragile. There are plenty of them still about. As the good example shows, they were made from Tange Prestige Ultimate Superlight (from 1992 onwards, and the eBay frame is a 93). Although it's called Superlight, the tube profile was 0.8-0.5-0.8, which isn't all that thin for a heat-treated tube. It was just called that because it was the thinnest tubeset that Tange warranted for mtb, but they were quite conservative. They did a road variant with a 0.6-0.3-0.6 top tube, and I doubt whether they've all rusted away. My Kilauea (Columbus Cyber) has a 0.7-0.4-0.7 top tube, which is about the thinnest that mtb tubes went until the advent of Reynolds 953 (stainless steel).
I don't think there's any link between the thickness of the tube and the propensity to rust, but there are variations in the alloying elements between different makers. My 97 Kilauea has Columbus stays and a chip in the paint that has been there for several years hasn't gone brown, but CCE has a 96 Kilauea with Kona stays and his paint chips go brown. Lots of frames have loose particles rattling around inside them, it doesn't mean they're rusty. Mind you, it doesn't mean they're not rusty either.
I don't know why they have a reputation for being fragile. There are plenty of them still about. As the good example shows, they were made from Tange Prestige Ultimate Superlight (from 1992 onwards, and the eBay frame is a 93). Although it's called Superlight, the tube profile was 0.8-0.5-0.8, which isn't all that thin for a heat-treated tube. It was just called that because it was the thinnest tubeset that Tange warranted for mtb, but they were quite conservative. They did a road variant with a 0.6-0.3-0.6 top tube, and I doubt whether they've all rusted away. My Kilauea (Columbus Cyber) has a 0.7-0.4-0.7 top tube, which is about the thinnest that mtb tubes went until the advent of Reynolds 953 (stainless steel).
I don't think there's any link between the thickness of the tube and the propensity to rust, but there are variations in the alloying elements between different makers. My 97 Kilauea has Columbus stays and a chip in the paint that has been there for several years hasn't gone brown, but CCE has a 96 Kilauea with Kona stays and his paint chips go brown. Lots of frames have loose particles rattling around inside them, it doesn't mean they're rusty. Mind you, it doesn't mean they're not rusty either.