how much risk of rain worth?

a lot for me

Millions of euros...

At the moment it's probably worth exactly as much as steam asks for it... I believe 9.99$?
However there is always a chance that for some reason after you bought it the game gets deleted from all other steam users except you due to some software/server error while at the same time the devs also lose the sourcecode somehow - and in that case you'll probably be able to sell your steam account with the sole remaining copy of risk of rain for a few thousands. My advice would be to buy it right now as the occurrence I described above might happen any minute now.

1.5 keys in steamtrade...

Tbh it is the best game I have played so far in 2014 so I give it a boost in my in my mind just because it's so worth the money

It was on sale for 3.39$ so it's worth 1.5 TF2 keys

I got it for 4 refined metal. (opening 4-pack)

Great game, yes its worth it.