For your door windows, you might check on the size of other windows that are currently available to see if they might fit your application. For example, here's a link to a kit for retrofitting JK half door uppers with sliders, perhaps they would fit your application:
http://www.retrofitoffroad.com/shop...retrofit-half-door-slider-kit-jeep-jk-2-door/. I have some here (I designed them for the company in the link) so I could measure them if that interest you.
Custom slider windows can cost $250 each or more, depending on the size and complexity of the window. One place you can have them made is Motion Windows (
https://www.motionwindows.com/). They have a quote request process you can use to get a price, it starts with this form:
http://www.rvwindows.com//wp-content/uploads/2015/12/New-Order-Summary-Worksheet-RV6.pdf
Rectangular slider windows are easier to come by, they are often available on eBay. I buy windows at RV Surplus outlets in the Elkhart, Indiana area (Elkhart is the Detroit of the RV industry). For example, the slider windows in my current trailer project came from a surplus outlet; they were about $25 each.