We use jetblue groups when I take my dancers down for competition. They are great. Unless you are within 30 days of travel it is $50 down and the balance about a month ahead of time. You also can change names up until the around the 30 day mark.
The rates will be slightly higher than the advertised rate for your flight however, it locks in the same rate for everyone. I tried booking a group of 11 w/o going through jetblue groups. Since you can't book all 11 at one time I had to split the group. When I did the first half got the sale rate that was advertised and then the second half the price went up because we had purchased the number of seats available at the sale rate.