Yes they are very expensive! I think I would go with the Alexander or Savic Plaza. Most Syrians seem to love the Alexander and it has the same floor area as the Savic Plaza. Access is better on the savic Plaza but you need extra shelves probably. It is frustrating when you want something bigger than 100 x 50 without paying extortionate amounts.
If you're wanting something with a deeper base as well, for lots of digging it does limit it to tank style or your wood cage I guess. Is he a chewer?
Or how about the Sky rat? You get a front opening door on the lower cage and lots of space.
I think they just import it from Germany (It's the Carlos in Germany)
Sky Rat 100