You generally don't have to pay for them. If you go to a dealer they should just give you an extender or two.I bought one for the work vehicle I have to drive during football season. I hate it only fits certain types of vehicles. I don't need one for my car. Generally I just avoid places that I know have small chairs or seats.
My Volvo V70 has a big glove box and a pretty spacious center console. It has lots of legroom, and decent headroom, but its hip room is pretty tight (designed for tall thin people). The extender works great for my big bellied 340 pound friend but doesn't help my big hipped 380 pound friend who really has to squeeze.I thought about this. But I drive a Toyota, and the glove box is barely big enough to hold the owner's manual ... all three volumes.