The Access runtime license has never been all that expensive -- the cost for the developer tools/extensions has been around $300 as long as I can remember (which would be as far back to the Access 2 Developers Toolkit, or ADT), but that gives you the ability to distribute your app with the runtime to an unlimited number of users. As long as your runtime app was used by three or more users, you'd have been saving money (assuming a cost of $100/user to install a full copy of Access).
The runtime for Access 2007 is completely free, but really, the cost before that was not all that great.
Marc Gravell added (in what should have been a comment, in my opinion):
Being free, though, is certainly an encouragement for people to try it out which the $300 price really would have discouraged.