One of my players has decided to make his own demolition charge rather than paying for it . How much should the components cost?

I have already informed him that he will blow him self up on a 96-00.

If you're looking for an official answer, you can find some extensive Crafting rules towards the back of the Inquisitor's handbook. However, as an ad hoc solution, consider asking the PC to pay 50% of the cost of the finished item in materials. We've found that to be easier for 99% of situations.