There was a big update to Battleborn last night so I assumed an announcement of free-to-play was imminent.
What they actually did was make the competitive PvP free. All maps and game modes are available to the free user, as well as a weekly rotation of 6 of the 30 total characters. The PvE missions and access to all characters still needs to be purchased.
If you decide to purchase the game after starting the free trial then all character levels and achievements will carry over to the full version. I know you can find physical copies of the console versions for 5 or 10 bucks. The Steam version is $30.
If you ever considered playing this game then now is a great time to try it out with no risk involved.