how much does it actually cost to be in a sorority

Dues range from $350-700 per semester, it depends on the sorority. And usually your first year the dues are more because of new member dues, etc. I think there's a look book on the Panhel website that should tell you more about dues. (The sororities that have cheaper dues generally don't cover as many things, i.e. you have to pay for formal additionally, whereas a chapter that has higher dues may include formal in those payments.) As for additional expenses, every frat event (6-10/semester) sells t-shirts as part of its competition, so you're encouraged/pressured to buy one, but it's by no means required. Big/little week can get a little expensive too.

Forgot to add: There are scholarships available though, through the sorority's nationals and through Panhel, and payment plans. It is feasible, I would go through recruitment and see what it's like no matter what. Then you can decide whether you can afford it or not after you've gotten the full information.

Freshman year expect to spend at least $1000 a semester. Dues will probably be close to $750 but the small things add up quickly. You will want to order sorority gear, philanthropy shirts, and pay for whatever outings are planned. Dues will go down over the years? But only marginally. Expect to spend around $1000 in addition to everything for big little week.