Ah, but then you could simply enslave some more people, or buy some slaves on the open market. Buying slaves to free them, while noble, does not solve the core issue. The only way we would agree to that deal is if you promise to never enslave a sentient being again, however even then 1 slave per revenue is an extremely steep price.
We are saddened by the Roman Empire's persecution of our organisation, as you definitely do not share the Slavers' ideals. Since you wish to find us, we wish you good luck, as you will need it...