I will soon be selling online student recordkeeping software solutions. Each client will have there own subdomain with the software attached to it. The pricing structure will breakdown as such: There will be a one time set up fee. Twice a year, each subdomain will be audited to determine how many students are being recorded. The client will be billed twice a year according to the audits. An estimated number of students will be paid for along with the original set up fee and then adjusted at the audit. There will be modules that can be purchased at sign up or throughout the year and with a recurrent fee for its usage (twice a year again). I need a solution that will allow for set up fees (fixed cost) as well as estimated usage fees (variable cost)at the same time. If this makes any sense to anyone, please let me know. I have been using amember for library subscriptions and course enrollment very successfully and was hoping it can handle this also.