We do have choirs for weddings, but most people prefer just to have a quartet of professional singers - one for each part (cost is one factor).
As for fees, its very difficult to say. It all depends on how experienced the singer is, how far they have to travel, how long the service is, how many pieces are they expected to sing, the complexity of the pieces (or do they even know it?) etc.
Sorry I can't be much help. Perhaps contact some of your fellow organist friends in nearby parishes who might have experience with this. They will be able to give you prices that are reasonable for your area/location.
Normally, we have it so that the money is paid in advance to the director of music and then this gets "redispersed" to the choir members and organist after the service. This saves having to chase newly weds for money, which can be a bit awkward (and it does happen).
Currently own:
ALLEN TC-3S (#42904 - 3rd Feb 1971) with Sequential Capture System
Speakers:
x1 Model 100 Gyro Cabinet
x1 Model 105 Cabinet
x3 Model 108 Cabinet