Your post sounds so familiar. I accepted a bid last year and my mom went totally crazy so I didn't pledge. Almost a year later, I still want to join the same sorority. So, I'm doing the same thing as you: researching, and getting up the nerve to ask again. I know that I'll be paying for most of the dues (all of it after the first semester). All of my friends and some of my mom's support my decision. I've also thought about just going through it without telling my mom, but I feel bad.
I know this: I don't want to get out of college regretting that I didn't go Greek....Hang in there (as will I). We'll get through this. PM me if you ever want to share your experiences.