As the sibling comment from androider says, after 6gigs is free, but after 15gigs you operate at reduced speeds.

Edit: here are the details: https://fi.google.com/about/faq/#plan-and-pricing-extra-high...

After six gigs it's free. It's great, my average bill is $30 because I'm on WiFi at both work and home.

Same, and even when I travel without wifi the data expenses are pretty marginal. If you download your podcasts, maps, and translation dictionaries before you leave, and you don't have to have youtube or netflix constantly playing when not around wifi, it's pretty ideal.