I do not know any GLO's that base dues on income, but i know that my chapter is very flexible in making arrangements with girls to pay their dues. Even housing corp was very reasonable if someone couldn't afford rent(YET many girls complained about living in the house---even though in the real world you don't get breaks like that nor do you get a cook!!!
-I'm the old house manager so I find that frustarating).
ASA also allows members to apply for scholarships through ASA. There are many to apply for.
Also my house decided to take formal and lower each chair's(social, sisterhood, etc) budget so that way when there are events that girls can't go to they aren't paying for it and those that do go only have to pay a few dollars or so except for formal which is more expensive.
I don't think there is any good reason to not pay dues. I knew girls who couldn't pay dues, yet could afford to go out to eat everyday and buy clothes that weren't on the sales rack. Anyone can pay dues if they work hard!!If they aren't paying their dues they cost the house more money!!!! If they can't pay it all at least they can work out a payment plan.