No one's going to mind unless you try to enter it in one of the cosplay contests and claim that you made it yourself.
Seriously, no shame in buying a costume if you don't have the time/skill to make one, so long as you leave the craftsmanship contests to the actual craftsmen.
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"If people are going to laugh anyway, I want to try to make people laugh, and then laugh myself."
-Emishi Haruki, Get Backers