Quantity   Component name
1 × Raspberry Pi Zero ($5.00) If I can get my grubby hands on one before christmas
1 × Stepper Motor Controller Breakout ($22.50) Adafruit DC & Stepper Motor HAT for Raspberry Pi - Mini Kit. Have an equivalent breakout for arduino and might be able to make it work with pi but this is more convenient
1 × Stepper motor ($14.00) Stepper motor - NEMA-17 size - 200 steps/rev, 12V 350mA
1 × 3D printer for structural components and pump or could machine them (your choice, ~$4 plastic cost)
1 × Aluminum chunk (free) To be made into pen body. Found for free in machine shop, could be wood from a stick in the yard in principle
2 × Cheap USB webcams (2*$4.16=$8.32) LE 20.0 M Pixel USB 6 LED Webcam Mic PC Laptop Camera (found on amazon for $4.16 each, free shipping)
1 × Plastic tubing (had some --> free ~ $3 otherwise)
6 × 1.8mm LED Bulb- UV ($16.95/50*6 = $2) Found on amazon - $16.95 for a pack of 50, I have a way of getting them cheaper
1 × Button (recycled/ already had --> Free)
1 × Wire (already had/recycled from dead electrical things --> Free)
1 × Total projected cost $55.82 + crap for shipping and taxes ~=$60-$70