Costs will be explained to you at recruitment. You can also call the office of Greek Life and talk to the director.
When I was at UCF, every sorority had the option to pay monthly and most members did pay monthly rather than in a lump sum. Doubt much has changed.
Socials are included in your dues. Extra costs would be t-shirts and sorority swag (Bid Day photo packages, sorority memorabilia, art supplies for making craftsy stuff, paddles, etc.). I have no idea what sorority t-shirts cost nowadays, but they varied from $5-$35 back when I was in school. I'd say I spent a couple hundred bucks each year on sorority extras. It's pretty much what you make of it. Fall tends to be more expensive, especially when you take a little sister. You don't have to go nuts and buy every single event t-shirt or extra that is offered, and the seniors usually pass down shirts and sorority swag to the newer girls. So there's that.
Good luck at UCF