Well as long as you let the carriers run the show, you're pretty much screwed. Here's a nice example from Finland, where there is a lot of competition between carriers.
For years the 3G plan prices remained the same between all players: 384 kbs plan for 10€ ($14) / month and higher speeds running up to I think 40€ ($55) / month. Suddenly the competition heated up again, and within weeks the prices dropped to 1 Mbps for 10€ / month and unlimited plan for - wait for it - 14€ ($19.50) / month. The amount of data transferred monthly is not limited.
I would suggest checking out Nokia if you haven't already. They are actually advocating unlocked phones. Nokia should be releasing a new phone running Linux later this year, and it is slated to top the N8 on hardware and especially software. It will also let you get root privileges without hacking, just like the N900 and the Internet Tablet line before that. I'm sure it will be slated in the press as The Nokia iPhone Killer, which it might be, but at least it will be a fairly open Linux running powerhouse of a phone that you can buy unlocked.