The free account is only good for a year, IIRC. Then you have to start all over again. Not sure if you lose your "place" in the queue at that point; I know (well, pretty certain anyways) that Delta and United's algorithm likes to see regular updates to the apps on file for consideration.

Everyone I talked to who got hired at United within the past year all had their apps in for 3-12 years. Here I thought guys were just throwing their names in the hat and getting called right away, but nope, the shortest timeframe for response for non-military, non-NASA, non-{insert minority group du jour here} was three years.

So yeah, you're better off just ponying up the dough.