Generally, your wholesale price you sell to retailers is about 50% of the retail cost since retailers generally like to mark up the products by at least 100%.
More information about barcodes and selling to retailers can be found here:
retailers related topics at T-Shirt Forums
Also use the search box at the top of this page to search for barcodes and you'll find several threads that talk about how they work and where to get them.
What wholesale price to charge retail stores for my product? 
