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I want to stick an LCD onto this little guy so that I can print standalone but the stock ones from printrbot's store are 100 dollars. Can I just grab an little LCD with or without an SD slot for 40-50 buck and force it to work on there with the proper cord? The printer already comes with an SD slot just no screen. Here are the printrbot's specs for those who know more about this type of stuff than I do:

"Electronics: Printrbot Rev F Printrboard with micro-USB connection (cable included) and micro SD card slot for untethered printing"

https://printrbot.com/shop/assembled-simple-metal/

It's hard to say exactly how the LCD is connected without some knowledge of the Printrbot electronics.
The Short version is yes it can be done, if you can figure out the pinouts, but you'll have to make up cables and some sort of PCB to mount the encoder wheel on. Before LCD's were common on printers I made up a board for a Mendel Max, having done it if I'd had the opportunity to buy one for $100 I'd have done that. I spent a lot of time trying to debug what turned out to be a bad LCD panel. I mounted the encoder on a piece of grid board that I cut down to size.

The first thing you would have to do is figure out how the firmware is expecting the LCD to be connected there are several different ways this is commonly done, including 8 bit, 4 bit and various serial options.