Harry Potter fans, your assistance is required!!!!!!!!!!!!!!?

Alright, so im going to the midnight release of deathly hallows part 2. My only problem is I have no idea who to dress up as! I Have MAYBE $30 to spend, and I want to be a cool character. I wouldnt mind being a more obsecure character either. I have a personality a bit like Luna's, she and tonks are the two characters I feel i identify best with. Im 5'3 , slim, with pale skin, grey eyes, and longish brown hair. I dont look that good with blonde hair so i guess luna's out. but i dont know who to be! my group of friends and i are part of our schools dumbledore's army, and pretty much everyone is going as their character, except me, becuase I dont have a character(all my favorites were taken). If it matters, Id either be a ravenclaw or hufflepuff. thank you! :D