Migrating 150k/8GB of e-mail to Google Apps for Domains

Because we're no longer using e-mail on a domain, we have an 8GB e-mail archive containing 150.000 e-mails for 5 different users. We need to migrate all this e-mail from a simple IMAP-server to Gmail. The error I am receiving when adding the POP3/IMAP accounts to Google via the web interface is: "There are too many messages on the other server. Please delete some mail from your other account, or move it out of the inbox.", so a more creative solution needs to be created. This 8GB of e-mails contains important e-mail, so sending this e-mail in a .tar file is not an option. There are 150K of e-mails in maildir-format. The server will be closed down in 2 months and we need to migrate before that. The most important thing is that we can easily search through 150K of e-mail. Google Apps for domains with Gmail is great for that! The solution should not be that hard. I am looking for a creative mind who has a good idea. If this project is completed successfully, you will also be my number #1 choice for future projects. Fast communication is of great importance to me. This project's budget will be $35 to $50, depending on the amount of work of programming that is required as it might just be a consultancy project. My preferred communication method is Messenger and e-mail.