The buying of airtran credits on ebay can net you up to 32 credits on airtran(128 coupons=32 credits) but that is the limit of points allowed via the promo.
Here’s a quick summary of what you can do with airtran credits:
One-way Business Class Upgrade: 4
One-way AirTran Coach Ticket: 8
Roundtrip Coach Ticket on Another Airline within the Contiguous 48 US: 32
Roundtrip Coach Ticket on Another Airline between the Contiguous 48 US & Alaska, Hawaii, Canada, Mexico:50
Roundtrip Coach Ticket on Another Airline Anywhere Else in the World:100
Free annual companion pass: 100
So, to get to 50 there’s a few options. (Besides for actually flying on a flight)
1. Open an airtran credit card There is a $39 annual fee. You get 6 credits for opening the account, plus 1 credit per $1,000 charged on the card(2 credits per $1,000 charged for airtran travel) And 1 credit per $1,000 of balances transferred, up to 10 credits, and a maximum charge for the transfers of $50.
Airtran Credit Card Linky
2. Gift Certificates Buy fully transferable, never expiring airtran gift certificates for future travel. For every $100 you buy, you get 1 credit.
Airtran Gift Certificates Linky
3. Rent From Hertz Rent for 2 days and get 1 credit and $5 per day off the rental, rent for 5 days and get 2 credits, and $5 per day off the rental.
Hertz/Airtan Offer Linky