few weeks ago it was about 1.5-1.7 FG/1m isk then it went down to 1.0 FG, and now it goes slowly up again to about 1.2-1.3 FG/1m isk
There is a high volatility when people with a lot of isk come here and when there is a lack of them.
plex price can simply be calculated by checking the ingame price for them in eve.