Well if you have 43 coins, it's time for a node !
.... and 600 coins for a Supernode!
I saw 500 !?
Yeah, both of them are wrong...

You need 42 ZEN for a secure node and 500 ZEN for a super node.
Also, these changes are slated to go into effect in late Q3 of this year, so plenty of time to keep mining. I definitely won't continue once an effective 30% tax is in place, however (ie - only 70% of each mined block will be paid out to miners).