1.) Max out on trial accounts.
-----a.) Open the regular trial account
-----b.) Have someone send you a bunch of recruit a friend requests, until your battle.net can't hold any more trial accounts
2.) Have an active wow account on the same battle.net account as the trial accounts.
3.) Get the trial account characters to level 5
-----a.) Park the account which SENT the recruit a friend at the human starting zone
-----b.) With all your trial accounts, just grind up a few mobs (will be super quick w/ 300% exp)
4.) Train Fishing
5.) Go to Darkmoon Island on all trial accounts
6.) Fish on each character until you get a sea pony, then learn it
7.) Log out & delete that character
8.) Log onto your active subscription account and cage the now learned Sea Pony pet
9.) Repeat steps 3-7 as much as necessary
I'm not sure if you can catch more than 1 pet per character, if you can then just skip the char deletion step. What happens here is basically you farm the pets on accounts which don't cost anything, and last forever. IF you have honorbuddy, I suggest using it. This method also works for grinding "The Bloodthirsty" title extremely quickly, as all honorable kills contribute to the account wide achievement.
I'm running 9 accounts currently, I'm at 140k honorable kills (started 6 days ago, from 0)
I have just over 200 sea ponies. Selling @ 200g a piece that's some nice profit.