Pretty easy to get them to 50 now if you can find someone or have a friend that already has them at 50 to HQ the turn in items. Even easier if you have the authenticator free teleport and find someone else that does.

Look up courier leves and turn in HQ items. Find someone with a free teleport destination. Have them set their free one to the city where you get the leves and you set it to the place the courier leve goes to. Free teleports back and forth. Saves like 20-50k gil. Get a level every 2-3 turn ins. Each turn in and grabbing the leve again takes about 15-30 seconds depending on load times.

It gets boring fast, but you get the levels really quickly.