I have been scrapbooking for 8 years and have attended many scrapbooking crops! To go about doing it, you might consider visiting a local scrapbooking store (if you have one in your area) or a craftstore where scrapbook supplies are sold. Consider hanging flyers in your church or where you work to let people know about your scrapbook crop. Charging 25-30 dollars a person sounds reasonable. However, when I pay around that amount, I also receive a few free materials such as cardstock and stickers.
The scrapbook crops I have attended are usually hosted by consultants of Creative Memories or Stampin-Up. However, I have been to crops held by scrapbooking stores. If you are planning on holding a scrapbooking crop, I would get on websites and contact scrapbooking companies or local stores. I am sure they can be of help to you so that they can set up tables to sell merchandise. Stores and companies may be more willing to attend your cropping if you charge them little or nothing at all.
As far as holding crops, I would contact churches (plenty of available rooms with tables and chairs), local community centers, indoor park pavilons, ect. I have attended crops at people's homes before but it sounds like you want a larger event so I would rule that out.
I hope this helps you. If you have any questions, let me know. I adore scrapbooking!