The "Werewolf Lord" from D&D prepaints sounds like it's ideal for you – it's immense:

Most of the other models are in the 28–30mm height range. Not sure what the ebay price would be for something like this, but I did get a similarly large giant from the range for about £6 (caveat: the price is based on rarity rather than size, so that might be a poor comparison).
If you want something more quadrupedal, there's the D&D Rime Hound, which stands about 40–45mm at the shoulder:
