Alerts & Reminder System Umbraco CMS & .Net Application

I am looking for a proficient web application developer who is experienced in c# and .net, we provide holiday websites with integrated booking solution. We would like an alerts and reminder system which will email a specific email when payments are due / overdue, I will provide the umbraco configuration and require the developer to build the module to interact with the booking records. We may require SMS integration on this in the future. Every booking within the system will have a start date and balance due date, we have customised email templates within umbraco. We would apply rules to these templates i.e Send 7 Days before balance due date. The system would then automatically email the client to remind them their balance is due. I am looking for someone with clear experience in this area, I will then supply a design document to complete the work and will expect a confirmation on the number of hours to complete.