The estimated time to do this project is 5 days.
Based on a fixed cost arrangement, and a completion date of May 30, the cost will be $1300US. A later completion date would allow a different price.
Before deciding, please check out http://www.imap.org/products/servers.html for a list of commercial products. The only product that I am aware of that supports virtual domains is the Netscape product. See http://home.netscape.com/comprod/server_central/product/mail/datasheet.html