I'm surprised and REALLY disappointed to hear that dealers are charging to install tether anchors. Everyone I've ever known who had them installed in an existing car was able to get it done for free. I thought it was mandatory that dealers do so upon a customer's request and do so without charge. 
Britax seats are the only ones that use tether straps rear-facing, and it's correct that those can be attached to any part of the car that's welded in (for example, to the rails that hold your front seats into the car). When the seat is turned around front-facing, however, it was my impression that the tether strap needed to be attached to a properly installed tether anchor to insure that the seat wasn't pulled at an unsafe angle.
I still think it's absolutely worth calling your car dealership and asking about installing tether anchors.
None of this has anything to do with LATCH, but it didn't sound like that's what the OP was asking about.

Britax seats are the only ones that use tether straps rear-facing, and it's correct that those can be attached to any part of the car that's welded in (for example, to the rails that hold your front seats into the car). When the seat is turned around front-facing, however, it was my impression that the tether strap needed to be attached to a properly installed tether anchor to insure that the seat wasn't pulled at an unsafe angle.
I still think it's absolutely worth calling your car dealership and asking about installing tether anchors.
None of this has anything to do with LATCH, but it didn't sound like that's what the OP was asking about.








