As one of the cheapest Scion owners I found, quite by accident, a very-very inexpensive front-center arm rest.
Because I am usually in the car alone, and because I don't like the front passenger seat head rest blocking the vision out the back passenger side window, I removed it. The front of the passenger seat usually has a cooler on it. The back seats are full or folded, and I didn't want to put it on the rear floor - or in the storage compartment.
While driving - carefully - I put it between the seats - pegs down, and positioned just like it was a head rest. There you have it - the cheapest dual purpose arm rest.