Mostly_Deals via eBay offers the Majestic Kids' MLB Player Name and Number Jersey T-Shirt in 42 styles from 15 teams (Prince Fielder/Texas Rangers pictured) for $6.50 with free shipping. That's the lowest total price we could find by a buck. It's available in select infant sizes from 12M to 24M, toddler sizes from 2T to 4T, and youth sizes from S to XL, although not in all style/size combinations.
Of note, a similar shirt in several additional teams is also available for $6.99 with free shipping. It's available in youth sizes S to XL, although not in all combinations.