@Ryan_Carlyle That’s part of the fun in challenging the standard norm of doing things 
@Shai_Schechter Instead of a full hall-effect sensor, you could just use a reed switch. Should be cheap – a small magnet glued to the belt and one component wired back to the controller endstop header. Not sure how the repeatability is though.
I don’t think a reed switch would be very repeatable, and I’ve heard horrible things about their reliability. If you look at the Cheap-O (https://www.thingiverse.com/thing:24189) though, there’s probably room to get the ~$2 BOM down. The LED and its resistor, for example, could be removed if you have an external testing apparatus, and you might be able to replace the other resistor with your chip’s internal pull-up. With these alterations and purchasing components in higher quantities, I bet you could get it down to your price range.
https://www.thingiverse.com/thing:24189