At least 3500.

Terms are,

Pool needs to be active for atleast 30days.

Anything i missed "myfarm"?

Edit, from the FAQ

Q.  Is it possible to create pools?
A.  If a pool is created, any miner can steal all of the blocks.  Theories have been put forth on ways to get around this such as coding in a collateral system, but none have been created.  There is currently a 3500 SPR bounty on the creation of a public pool that successfully runs with no stolen coins for 30 days.