Just to clarify. Ive had a few questions on what would be included.
What I would include for $40 would be the 4 brackets CNC machined from 6061-T6 Aluminum. You will need to buy nuts and bolts along with the seat tracks from FFR.
In addition you will need to make the handles to adjust the seats. I made them out of flat stock. .1875" - .25" x .75" flat alum or steel stock would work well. Because there is no room for cables you will end up pushing down on one and pulling up on the other to slide the seat. It works well once you get the position of the handles right.