Matt,
I would think that a "good" used backhoe would cost more than $2K-$3K (more like $3K-$4K, but I haven't priced any recently).
I remember pricing a new B2150 w/FEL in 1998 for around $15,500. I'd guess that the B2150HSD/FEL/BH combo would've been around $21K new, so that $17,000 for a very good used one would seem reasonable (but not a steal).
Note that I am assuming that the B2150 is hydrostatic, and not gear drive.
For comparisons with today's Kubota line-ups, the B2150 would be between the B2410 and the B2710. Get a quote on both of them with FEL/BH and see how it compares with your $17,000 quote for a used unit. Compared to the B2150, the newer tractors are quieter and have the flat deck.
B2400/B2410: 24 hp / 3-cylinder / 2 range HST
B2150: 24hp / 4-cylinder / 3-range HST
B2710: 27hp / 4-cylinder / 3 range HST
Kelvin