About two to three months worth of lease payments on a 190 would cover the purchase price of a F100 at the prices Alliance paid.
Over the course of a year you could buy outright 4 F100's and own them vs renting an E190.
There are good reasons to buy a new airframe when you are operating high frequency RPT but for charter/FIFO where you do a morning and an evening push with the machine sitting around the rest of the time a depreciated airframe is hard to beat.
Given that contracts typically don't last as long as leases I.e. You don't see many fifo contracts last the 10-12 years that a typical new airframe would be leased for, so you take on a lot of risk buying/leasing a new airframe for FIFO work. Obviously Cobham got the guarantees they needed to take on the 190 they have, but it is no surprise that most FIFO work is done with older airframes.