I could be wrong but I was told by my dealer that even though the fm-750 is case ih branded it is still all trimble software meaning it would need a trimble flashed nav 2 - which in turn would not talk to a guidance ready mx245 (since it would have a case ih accuguide kit rather than a trimble autopilot kit)

I think (again and I could be wrong) that your only option for a display that would work with your guidance ready tractor would be a pro600/700.  I'd check out the classifides section here.  there are a lot of used navs and gps recievers and even some pro 600's that come up for sale a lot under list price that still work perfectly fine.