Also consider GLBT group cruises on mainstream cruises. They are quite a bit cheaper, and an easy introduction.
I am leading a group of gay men on a Carnival Cruise in January 2011. While we are all gay men, you would be welcome! We are all sold out of our initial allotment, but Carnival has just announced some good prices you might want to take advantage of, and you can see the details at BajaGay.com - July 1st UPDATE -- Price Reduction! If for nothing else, good for comparison.
Groups get advantages and cost less than the gay/lesbian only cruises... the GLBT exclusive cruises are great... they cost more, but they provide more. It is just a matter of your preference... perhaps you want to try both!
Look around... you may find a lesbian group you prefer over our group. If you have any questions, I'm happy to help!