Im not sure who told you that or if something has changed in the brief time that Ive retired, but you most certainly will have to pay. Unless you are using the GI Bill at an university where you are enrolled in an accredited flight program (Post 911 GI Bill) or you are enrolled in a Part 141 School (Montgomery GI Bill) the GI Bill will not cover the ATP. The Montgomery GI Bill will only cover 60% of it at the inflated rate a flight school will charge. Has something changed? If you have some flight school telling you that, I would research it. If you know something Im missing here please let me know.

If you are hired at a regional and have the minimums along with the written test completed, the regional will "pay" for your ATP by putting you through their training program.

The previous advice given here is pretty solid. You want to have your instrument proficiency SHARP SHARP SHARP. Spend some time on Microsoft Flight Simulator. Actually spend a ton of time on Micorsoft Flight Simulator. Know your Jepps and review your Instrument Flight Manual. Good Luck!