I recently picked up a vintage Canon nFD 50mm f/1.4 lens on eBay for around £100 and adapted it to my Sony A7iii camera body using a FD-NEX mount adapter (£15). I also added a basic, slightly stretchy 62mm 3D printed follow focus gear to the lens’ focus barrel (“Seamless” branded from Amazon, £7.50) to make it easier to focus behind the camera with a follow focus (Neewer £25). Here’s a test video:
Note: the opening/exiting wide-view shot wasn’t on the FD 50mm (that was the 28mm FD 2.8) and a “Meike” 10mm extension tube (£20 for a set of two) was used for the close-up shot on the pen.