The guarrantee is that if they work, I keep them, ones that dont work get sent back for a instant replacement, given shipping time etc.
As a guide to cost, I used apx 40 LEDs to do the playfield on TEENAGE MUTANT NINJA TURTLES. Thats a total cost of less than $10 to do the whole machine. BARGAIN !
If u calculate a machine that has double (80 x LEDS) thats only $20 per machine or up to $40 for a 160 LED machine. Those LED kits u see various sellers selling at $200 plus can be a little expensive, even if u calculate and add the flashers in. You are best to buy LEDs in bulk, and fit and do your own kit.
As a guide, I place red LEDs under red inserts, green under green inserts, white under white etc, and purple under purple etc, BUT i use white under orange mostly and white under yellow mostly. Some yellow or orange inserts look better with white under compared to yellow or orange etc. Just experiment etc.