At BTC = $6 - you need 567.8GH/s to make $1mil in a 365day year with free electricity ... (3,333.333 blocks at current difficulty of 1250757.7392747)
Which equates to 710 singles (at 800Mh/s) mining non-stop for an entire year ... and their fans not failing and never over heating coz they have no way for you to know this - they will just pack up and die without warning.
Of course if you had 8,518 of them you could do it in a month
i.e. $1mil a month is ~6.814TH/s at the current difficulty.
Assuming nothing else changes; the addition of this many bitforce singles would increase mining difficulty, you would need even more.
It also depends on if your 800MH/s is 800,000,000 or 800*1024*1024.
Here's the number of singles I get after calculating how much higher the difficulty becomes, note this is 800MH; if spec'd at 800MiH/s you need more.