Mostly Deals via eBay offers the Majestic Men's MLB Player Name and Number Jersey T-Shirt in several styles (Washington Nationals/Bryce Harper pictured) for $15.50 with free shipping. That's about $14 less than you could expect to pay for such shirts elsewhere. They're available in select sizes from S to XXL, although not in all style/size combinations.

Note: When browsing styles, it easier to select the "Player" filter first.