There's a ton of information on GreekChat that can help you. Do a search or three.
You will face a lot of challenges if you are the only unrecognized GLO on campus. As others have said, you won't be able to use campus facilities, advertise, participate in Greek Week, etc. depending on your school's rules. You'll face challenges during recruitment too - women will wonder why they should join an unrecognized GLO when they can join a recognized one.
There are lots of national/regional MCGLOs out there. Keep looking; you may find one that is a fit.
Can you be recognized as a local sorority if you state that your ultimate goal is to affiliate with a national within the next few years? It takes time for a local group to affiliate with a larger org.
If you do operate as a local for a while and then affiliate with a national, you won't necessarily lose everything. For example, I was a member of a local that became part of a national GLO. My chapter still supports the philanthropy we chose as a local. What you can and cannot keep will depend on the national.
As for dues, put together a budget. What do you want/need to spend on recruitment, ritual, sisterhood activities, formals, t-shirts, badges/pins, etc.? If you hold fundraisers for charity, keep in mind that you could lose money, so set aside a buffer for that. Then make sure your dues cover all your expenses. If you find that the dues would be prohibitively high, trim back the budget.
Good luck.
