You might want to keep an eye out on Ebay...or even post to the Want It Now section.
Depending on your pup's size, you might be able to alter a youth jersey...they are pretty reasonable on Ebay.
There are also infant onesies....maybe alter one of them?
Here is a link to one ...
Emmitt Smith Youth Jersey Dallas Cowboys Reebok onesies - eBay (item 230360831753 end time Sep-23-09 09:01:15 PDT)