The single supplement isn't always that bad, especially if it's just a group vs. a whole ship. Most of the group prices are close to the online prices so if you shop that way you can get a good feel for the price. For the one I am going on next month, there was no single supplement. it's a bit convoluted with the various discounts I got, but in a nutshell, the price quoted me to book with the group was about the same as the online price, which allowed for no supplement. The agency that books the group was not able to book using all the discounts I had but told me or a small fee I can link my reservation to the group, which I did. Since I am traveling solo, the value in this for me is being able to dine with the group and go on excusions with the group, if I choose.