They were only added recently, thats why you might not have gotten it before. And, you have to have the money at 1 point in time - for example if i put 200k into my forum bal, I'll get the trophy, and if I take the 200k out, then i'll still have the trophy.
And no, it doesn't have to be exact - I could put in 200,005 and still get the 200k trophy.

 

^

The trophy points only apply to bank balances past their introduction. Andrew answered that question in the shoutbox yesterday - basically, it's not worth the effort to go through absolutely every forum member's transaction history, calculate their maximum balance and then manually award the trophies.

At least. I received 15 bank balance trophies at once because my bank's value is at $1.09m.

 

Your balance is at $599 right now, so I assume you transferred the money either to another player or back to your balance. Based on previous experiences with rating/post trophies, they usually take a few hours to be applied (i.e. removing the money from your balance before the trophy update will cause your previous balance to be ignored).

 

Then that's a bug...