I don't think they're going to give them away, I think they've got two options they'll pursue: 1) they'll do what they've done with the Nexus tablets and phones and sell them for as close to cost price as they can to get them out there, or 2) they're going to take advantage of the fact they'll be pretty much either first to market, or most desired and charge a reasonable markup on it.
Option 1 makes sense, Google's core business is monetizing your eyeballs. It's almost literal in this sense. Glass is going to have some form of advertising and Google has always wanted more data points and more ways to show adverts to you. They make a lot of money on it.
Option 2 is a bit out there for Google, and represents a business strategy shift. What if they can also become a respected hardware-software manufacturer? They've got as much brand awareness as Apple, they're building a reputation for devices as well. Glass could be phenomenally popular, so we're talking a whole new market share that could explode. That could make Google a serious amount of money if they were sticking a 30% markup on (lets be honest, they could do an Apple and go higher on it as well). It'd help them diversify so they've got advertising as a core, and a potentially large revenue stream from the hardware on top. Money in the bank helps pay for the next Moon shot.