You can get 21 sports jerseys very inexpensively if you are willing to spend some time looking around online. The problem is most people are looking for the cheapest possible prices, which is what they can get on the internet. If you are serious about finding the best jersey that will fit you perfectly and will give you the ability to wear it year after year, you should be looking to purchase from a specialty online sports shop.
If you don't want to purchase a cheap jersey, you could try searching for sports stores in your local area. Some people buy their favorite team's apparel from these stores. They may even sell other great sporting goods that you would not normally find in your local stores. You could also check online for stores that are selling sports apparel.
Don't buy a jersey that you will have to throw out, especially if it is an expensive jersey. It will take you years of wearing it before you can really appreciate the value of your new apparel. When you do, you will probably want to buy the jersey right then and there and not have to look around for something else to wear when you get back home.