Alrighty, I am pretty much in the same boat as you lol, I am doing a Chii and Freya cosplay for Otakon 2005 also ^_^. For ears, check Ebay, you can usually get some good deals for both the ears and the hair spools.But if you are on a low budget, go to google and search 'chobits ear tutorials', and just choose the tutorial that works for you the best. And to refer to the question about Chii's wings, yes she does have angel wings on her back. To do these wings I would suggest either buying a temporary tat that is similar to the angel wings on her back, or getting them professionally airbrushed on, or if you have an artistic friend or relative, have them draw the wings on. I have even heard of people using eyeliner to do this (which, as it turns out, works pretty well). For reference pics: check this site out: www.dragonfly.mindlinkcore.net
they have scans from the Chobits artbook and a bunch of links.