Dunno about under 50. A decent titanium or quartz nail insert for an enail coil will run at least that.
However...for the actual controller....
@Mañ'O'Green did a DIY rosin press thread, and the PID controllers he used were like twenty bucks or so on Ebay. One of those with a project box and the a female connector to match the connector on a enail coil and would be good to go. Under 50 would be hard for everything, but should be able to do just the controller for that. And definitely get one built for way cheaper than the several hundred they sold for last I looked.