How to make a rapunzel wig?

So my school is having a dance where we are dressing up as movie characters, and I want to go as Rapunzel from Tangled. I already have a pink dress and blonde hair and I don't need shoes so.... all I need is hair extensions. I just want it to go to maybe the floor so obviously not as long as it is in the movie. I don't have much money or means to get anything. How can I make myself a wig?? It doesn't have to look super legit. I was thinking of just buying a ton of yellow yarn and maybe making it look like her hair when she had it all braided back with the flowers. So my question is how do I make the yarn wig attach to my head? Whats a better way of doing this since that would be a TOOOOON of yarn (her braid is really really thick)? Thanks for any advice and help!!