I think we can get an idea how much the WOF RP bonus cost them by looking at the last week's lottery numbers. If you compare round 332 and 333 you can see that the total number of tickets for round 333 went up significantly.  It's reasonable to assume that people got at least 100 million lottery tickets from WOF spin bonus that was introduced that week. Since WOF rewards were distributed evenly between lottery tickets, satoshis and reward points it's reasonable to assume that people also got roughly 100 million reward points and 100 million satoshis. That's 1 full BTC in immediate payouts and another one in delayed payouts (when people reach 100K reward points and convert) in one week. They had to shut it down quickly.