Message for HITCHHIKE

Please help me clear up this doubt once and for all!
would you say :'it's us who HAVE to pay' or 'it's us who HAS to pay'?
I guess I'd probably say "who have..", but I read the second example in some book a few days ago and I want to make sure that it's either an acceptable form or a mistake and as such to be avoided (I doubt it though, as I read it in a novel written by a former English language teacher, notably NICK HORNBY)
Thank you, and please, BEAR WITH ME!