Personally, I've thought of a rather nice solution, that is consistent with what Greg's done in the past:
We have established that there is an incompatibility between IC2 bronze costs and Forestry bronze costs. Greg has also been willing to get the Railcraft Rolling Machine involved in the mixed metal ingot recipe, so there is precedent for what I'd suggest:
Perhaps one of the two 'families' could use regular bronze ingots, while the other could use 'rolled bronze plates' or similar. This would allow for a roughly similar recipe for the items, while permitting a change in cost. Personally I'd prefer to have IC2 items require 'rolling' - after all, IC2 hardly uses bronze at all. This causes trouble when you consider the IC2 wrench, which should remain fairly low-tier. It is a rather sensible solution for the armor - of course, it raises some rather strange questions about 'vanilla' armor.
Alternatively, one could have 'refined bronze' - that is, bronze that is reduced with a furnace - but that seems less elegant, somehow.