Location is a big factor in the US. If you're in or within the general orbit of a big tech-heavy city or region, then you're likely to run across a lot of stuff frequently. If you're not, then $75 for a stock 6360 doesn't seem that unreasonable.
The "desirable" Macs have been able to fetch a couple hundred bucks for a couple years at least, so I don't see $75 as being unreasonable for something "ho-hum, but unique and not widely appreciated." So, if you want one for the purpose of having a 6360, then I'd say go for it. If you've got the $75 laying around. They're unlikely to get much cheaper.
Granted, if you're in, say, San Francisco or Seattle or even Portland or LA, I understand that the feeling is likely that there's a giant pile of them somewhere you just haven't found where it'll be in the $0-5 range, so at that point the question is whether or not you want to spend $75 on it, and not whether you want it at all. (Although as the years progress, each time "this is the last one you'll see like this!' has a higher possibility of actually being even a little bit true.)
Just casually, eBay in the US appears to have three 6360s on it right now:
- A complete kit with a multi-scan 15av for $399
- Two more, one for $165 and one for $199, in close to stock configuration with no accessories
I know i say this in every single "should I?" thread, but: If you want it, and you think $75 is a price where you wouldn't regret it, do it. You found one at half what the next least expensive option for this machine is, nationally. If yours includes anything or is specifically known to be working, then you're already ahead of where most of what's on eBay is.
I understand, though, that it's tough, because you already have other machines that need your functional needs - it sounds like this might primarily be an aesthetic/completionist collection item. (Which I understand entirely: I want one too, even though I also have other machines.)