There are three (3) different models in the RB line. The 'RB Pro,' the 'RB Pro S,' and the 'RB Pro SD.'
The 'RB Pro SD' is the latest and probably the most desirable.

Lenses for the RB line were also available in about three (3) different levels.
Early 'non-C' lenses with very little or single coatings, the 'C' lenses with multi coatings,
and then the best/latest, the 'K/L' lenses.

If I were starting a RB kit, I don't think the 250mm lens would be a desired focal length, early on.

A 120 film back will be more useful to you then a 220 back.
As mentioned, do ensure a view finder, WLF preferred, and focus screen are included.

RB manual:
http://www.butkus.org/chinon/mamiya/...ofessional.htm
RB Pro S manual:
http://www.butkus.org/chinon/mamiya/...rb67_pro_s.htm
RB Pro SD manual:
http://www.butkus.org/chinon/mamiya/...b67_pro_sd.htm
Old RB accessory manual:
http://www.butkus.org/chinon/mamiya/...ccessories.htm

Check prices at KEH Camera, Georgia, USA.
http://www.keh.com/Camera/format-Med...de=RB&bco=556&

Prices from KEH, minus about 30-40 percent will give you a fair average of the value of used camera gear in the USA.
(Odd...as of this posting, KEH does not show any RB bodies on hand/in stock).

Marc