Flea collars suck, we would usually pull them off the dogs/cats that came in because they tend to get irritated.
It's off-label use, but at animal control we would buy packs of revolution for huge dogs and then individually dose it out for smaller animals. I know one pack of the 120 mg/ml concentration of revolution for extra large dogs (3 doses in a pack) was enough for about 24 adult cats when you dosed it out, so it ended up being really cost effective for us. We used to recommend the same to some people in our community with low funds but a large number of animals (our city ordinances allowed for up to 6 pets in a house) because otherwise they just wouldn't use flea control at all and their animals would all get sick. Revolution is a pretty great product, though unfortunately it doesn't control tapeworms (dang cestodes!
) so if you have already seen fleas on your cat you should keep an eye out for any wormy friends she may have picked up.
Of course, it's one of those things that you should definitely talk to your vet about before doing (especially to make sure you're getting the dosing right and not medicating the heck out of your cat), but in the long run it can be a viable cost effective option for flea control.
Here's a little information on it from UC Davis' Koret Shelter Medicine Program:
http://www.sheltermedicine.com/library/selamectin-revolution-dosing-chart