Harry Potter Costume Help?

Hi, I want to go as a Harry Potter student for Halloween, and I looked for a Ravenclaw robe (im a ravenclaw!) and found one place who sells them online.........for 185$$$ ummm no thanks.... so i bought a 25$ dollar one from party city, but ists a griffindor one! so griffindor colors are red, and ravenclaw colors are blue....how do i change the fabric lining the sleeves from red to blue?? cut them out??? would a tailor do it??? also the hood lining is red......the seal is not a problem (iron on a ravenclaw one) so an answer would be appreciated thanks!