I'm trying to move 30 user OES site with 16 live users

GW2012Sp4 - (no GMS)

budget is limited & instead of a new Server they have decided to adopt Office 365 with OneDrive
They have less than 100Gb data + GW data
An access based sales system is being ported to Web Application (about 80% done)

Anyway, I'm looking at a cheap way to get the Email exported - I need to explore Outlook IMAP practical ?
Most GW > Outlook tools seem to cost $900
some of the mailboxes are large ~ 15Gb... is this doable?
Addressbooks can be exported to CSV

Have I forgotten everything ?