Used HP100s are almost impossible to find around here, and, if you do, they are the Faber HP100 (not Faber’s FX100), also referred to as the M Series. These have a completely different set of specs than the other 100s. First, they’re rated with a “+”, or you don’t get the extra 10% to get to 100 cf. Second, they are beasts both out of and in the water. Empty, they weight ~ 4.5 pounds more than the FX100. They have a full buoyancy of about -14.75, and an empty buoyancy of around -7.25. Third, they are top HEAVY, even underwater.
And this is why I typically use my LP85s and not my 100, even though @formernuke is spot on about fills.
Erik
I do not own any Fabers... I know they're a different animal. As said, mine are all Worthington or PST.
I'm not sure what the market like is up there, but all my tanks have been bought used from craigslist or FB market place.