Type 'D' FE buses tend to cost $10K more per bus than a Type 'C' with the same number of seats.
Type 'D' RE buses tend to cost $10K more per bus than a Type 'D' FE bus.
As a consequence there just isn't as many RE buses for sale used because they just don't sell as many RE buses. For every one RE bus sold there are twenty Type 'C' buses sold.
Since they cost more new and are preferred by convertors the RE buses tend to cost more used as well.
The TC2000 was equivalent in value to the Saf-T-Liner MVP. Both were built with lighter duty axles, power packages, brakes, etc. than the All American or Westcoaster. The TC2000 and MVP came in both FE and RE versions.
As far as why you seem to see more Thomas than BB's I can't tell you why. I see an equal number of each.