pre-Halloweenie

I've been looking for a Halloweenie costume for Aria. Not just any costume but a specific one because Aria already knows what she wants to be. I know it's a little early still but I think I should get started on the search or I'll surcome to defeat. All previous Halloweens I was the one who decided on what she should wear because she was too young to tell me otherwise. Both years, I dressed her up as a white bunny (2 different costumes, I have a thing for bunnies). Well this year, Aria wants to be The Little Mermaid. I've been looking online and it seems like most of the mermaid costumes that I find at least $40.00, ouch. What happened to the good old days when I can get a great costume for less than $20???
I love my daughter and I will get her the costume, just not for $40.00. The search continues.