I bought an LED kit from eBay (blue LED’s - but you can get any colour) and it can with full instructions and all required resistors (it’s only for the pop-up light) and heat shrink.
From memory it was <£10…
3mm leds are about 1.5USD per 10 pieces. Resistors (680-1000ohm) are about 1.5USD per 10 pieces. That’s 60cents per pair 
5mm ones goes for the strobe light and 33/45-buttons, no resistors needed
These are good for the pitch, no resistor needed:
edit: I remember modding my first deck with blue leds over 10 years ago. The leds were 20€ per deck back then!
Bumping this as I look for an answer for my MK5 pop up light. Anyone???