The GC coins per month? Just did my first month extension.(and thanks to Zen's excellent advice, possibly my last.) Cost 30 gold coins for the country, 30 gold coins for the enterprise on FB. Same price.
If you're asking about product prices, per capita usage of consumption goods, I haven't really paid attention to the price flucuations between worlds, as I am not set yet to be a major commodities player.
As you know, with it being the war world, the risk is much greater. If you are going to go with permanent war protection to secure your main, then that is an additional GC cost. 2GC per 4 game months. (7.5 per real month, roughly, so 15 more GC). (same for all countries on FB, 2x cost of the other worlds.) The big beater sticks costs no GC, but lots of Sim Moolah.
Hope that helped,
MNey