I'm currently developing an invention that will require a small displacement probe to measure 3-4 inches of range with no need for a lot of accuracy (its not a professional or scientific application). The main problem is that it has to be no more than about $30 when purchased in bulk, preferably a good bit lower than that. I would like it to output to a small LED screen. Does such a design exist? Is this something an intelligent person as myself could possibly hope to build? Thanks for reading, hope you can help.