Ah, I didn't know you were actually considering doing it yourself. That changes the complexity issues to: Doesn't really matter as it's your own problem to deal with:)
Anyways, that's a bit hard to say without actually knowing the exact implementation. I was speaking in general, because you are giving the system power to change. Without very careful control, it is possible for that system to get into a state that you didn't anticipate. Typically, the more likely scenarios usually make the system useless, rather than exploitable though. The most likely issues would arise from potential errors in the formulas and how rounding would be handled. Over time, even very rare very small rounding errors can compound. So, to help avoid this, I recommend using as little division ( or multiplication by a decimal ) wherever possible. Try to stick to addition and subtraction of integers to avoid rounding errors.
It would also help to increase the base EMC value here as well. IE: Cobblestone being 10 or even 100 instead of 1. This both makes it more flexible for what division or multiplication you might need, but it also means individual changes of 1, and by extension any off-by-1 errors, will have less impact on the system.
If you want to email me so we don't derail this thread, you can. My email is zemerick13@yahoo.com
If I find some time I might even try mixing up a bit of a starting formula for this. It could be interesting.
Have you decided what range of EMC materials to include in this? There are quite a few items in total in Tekkit, which could take quite awhile to add in. Perhaps start with just the base raw resources? Finally, for crafted items, are you planning on keeping the items separate, or having the price of the base materials affect the price of the crafted item? This could get very complicated, very fast.