Airplane operating costs don't vary too much, but in high-cost metro areas there's always a premium for anything and everything. So you're probably looking for smaller or mid-size towns.
Also since you know you need a block of time, you can probably find someone who will rent you a plane for a large block at a significant discount. That's better for the owner and plane than having a parade of random cats flying his plane on training missions. If you're doing mostly XC, even better... that's a lot easier on the plane than primary or CPL training.