Based upon prices that I have seen, if your
B7100 is in pretty good shape then you could reasonably expect to get between $3000 to $4500 depending upon several factors (such as the area of the country that you live in).
The advantages of the BX series over your B7100D is hydrostatic transmission and power steering. The BX series has a water pump for the cooling where the
B7100 does not (the "water-pump" looking item behind the cooling fan is the alternator). Recalling from memory, I belive that the BX has a temperature guage the that
B7100 does not.
Advantage or Disadvantage? The BX does not have left&right wheel braking options as does the
B7100 (I never use differential braking on my
B7100 anyways). The BX does not utilize a clutch pedal. The BX is physically smaller but has a higher HP engine. I don't have my
B7100 manuals in front of me, but I beleive that the BX series 3-point hitch has a lower lift capacity than does the
B7100.
B7100 and BX series similarities: Neither tractor has a Tachometer. Neither have position control on the 3-point lift.
Will the BX adequately replace you
B7100? It mostly depends upon what you do with your tractor. With the exception of the 3-point lift capacity, I believe that most other differences favor the BX or are nearly "break even".