Well i've been thinking about a decent ratio cause I've played both D2 and eve quite a lot .
CCP (eve devs) sell isk, more exactly they sell GTC (game time codes) u can resell to other players for isk. I used to pay for my play time this way, buying GTCs from other players when my wallet and ship hangar were both fat
I think when i stopped playing actively, a 15$ GTC (30 days) was worth about 180M isk ,maybe a bit less. Iirc u can buy FG from njaguar at a 250fg/10$ rate (correct if im wrong) ?
That would mean a decent isk/fg ratio would be about 120Million isk = 250 fg (=10$)
-> 1M isk = about 2fg
Hope this helps