Replying to Nikon to Canon EOS lens adaptor ring

I have searched this, and have found nothing of any use so sorry if this is a repost.

I have been researching lens adaptors/mounts so I can use my 55-200mm Sigma (for Nikon) lens on my Canon EOS 550D (t2i). I have found various different options, but the price difference is just ridiculous!

For example:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=290467767933&fromMakeTrack=true

and:
http://www.bhphotovideo.com/c/search?Ntt=nikon+to+canon+lens+adaptor&N=0&InitialSearch=yes


Has anyone on NS used an adaptor ring and would recommend one? Or tell me why there might be such a drastic price difference as I can't figure it out.

Thanks in advance, and sorry for the long post
-tom.skier