Caffeine

I think this has been touched on a couple of times but with no clear answer for me, I want to make my own cola to save money. I spend about 50 dollars a month on cola and I can cut that down by making my own, I work at a brew on premise where we have all the ingredients and equipment I need. All I have to buy is soda extract, my only question is how to caffeinate it?! I've heard get the pills or powder but I don't know where a good source is or a good product. The ingredients I will use are :
Water
Sugar
Sparkling foam( from yucca)
Wheat malt extract
Cola extract

All I need is some info about caffeine, any reply is appreciated greatly

You can order it online from a host of sources...pure caffeine powder.

Smartpowders.com is a reputable source for lots of bulk powders.

Amazon.com has it.

Thanks I found one that I think I will be really happy with I hope the cola turns out well

Let me know how it turns out, I'd love a cola on tap.

If you drink that much a used bag in box/fountain system may be a better choice in the long run.