I'm fairly new to ESO recently so take this with a grain of salt... but in game people are selling 1k crowns for 1million igg and you can get 1million igg on here for around 450fg
So that should give you a general idea
granted, i have talked to a few people in game saying crown prices have spiked, 1 crown used to be about 300 gold and now its running 500 gold.. so maybe the price is a little inflated right now.