Here is some points about jerseys.
The Swingman line of jerseys has been around since about 2000/2001, under Nike, Reebok and Adidas. All 3 brands have maintained more or less the same quality and size, except Reebok and Adidas have 2 inch droptail at the rear of the jersey. Nike ones are probably a tad smaller, but the difference isn't much. If an XL Reebok or Adidas swingman fits you, then a Nike one will as well.
I find the Swingman the best of all the jerseys, because Authentic jerseys are a lot more expensive and also have the horrible horrible horrible (did i say horrible) shiny look to them, and actually look cheaper than a Swingman! They also sometimes come with the terrible wide shoulders that are the new fasion for some reason. Much like the cheaper replica jerseys, they look more like a vest than a singlet.
$50 for a New With Tags Adidas Manu swingman is ok, not great, but not bad at all. I got a NWT NIKE Parker Grey Swingman the other day for $17US... so it depends on what you are searching for and what brands. I often prefer the Nike versions because it is the exact same product as the newer ones and are a lot cheaper. If you search hard enough though, you can find brand new Adidas stuff for cheap to. I got an Orange Cavs Retro for $19US the other day. But you do have to be careful, because there is a lot of fake going around on Ebay... if you have any more questions or are looking at a particular item and wont to know if its real or not, feel free to PM me about it.