If you'd like to pay an extra $3 to use their image upload interface to create a CafePress infant bodysuit you could make at Cafepress.com for $9.99, then hop on over to MakeAOnesie.com.
But you'd better hurry before Gerber's lawyers hear about it. Onesie® is a trademark of Gerber Childrenswear, Inc., a company with a history of vigorously defending their brand assets, pursuing even the most insignificant blogs and demanding they stop "misusing" the term Onesie®.
CafePress's infant clothes are not Gerber, so technically, they're not Onesies®.
Meanwhile, if you're looking for a trademark-violation-proof way to print free money three dollars at a time with a jpg generator script, MakeACreeper.com and MakeAOnesie-StyleInfantBodySuit.com are still available as of this posting.