If those 1 to 2 million are for the SE 210 10B, GET 'EM!
For an F-27, 2 million sound a little bit too much. When the world is young and planes are scarce, prices go up quite a bit. Still, I'd recommend you stay away from leases that are over 10% to 15% of plane value. Also, unless you're based at big airports, don't lease anything for more than 4M or 5M, tops.
Start small. Lease an inexpensive plane and put it in service. See how much it makes. Is it enough to pay for the lease AND for the needed gates while still leaving you a nice margin? If so, you'll start to have an idea of how much you can pay. If not, give the plane back toward the end of the month.
Regarding discrepancies in plane value, I suspect there's still a bug somewhere in the system. I'd suggest posting the question in the Bugs section.