Frankly, as a parent and an educator, I would welcome uniforms!
I work in a middle school and see so many problems with even trying to enforce our dress code.
Having the kids all wear the same thing allows the kids to concentrate more on their schooling, than on who has the "cool" brand of clothing on, or whether someone will "like" what that person is wearing today.
They are limiting your choice of polo colors to help reduce the "gang" colors... even in our community, we get kids in middle schools that are members of gangs... we have to watch for certain colors, certain insignia, certain doodling. It is amazing how prevalent it can be, even in our "safe" city.
You don't have to buy from that vendor..... be assured that you can buy it MUCH cheaper from Target or Wal-mart..... the school isn't going to care what place you order from, but they are giving you the name of a vendor that is set up to supply what could be VERY large orders since it is appears to be district-wide.
At any rate, you don't have to order from the vendor... check online places to see what kind of prices you can get.
Truthfully... your life WILL get easier when you don't have to battle over whether an item is "school appropriate".