you can buy the entire sensor with a new cap from alibaba. I struggled with this a few years ago. same situation as you. That was the only route to go cheaply. Even then I think it cost 30-40 dollars a sensor. I can't remember.
You have to beg the seller to sell you one or two, because they will try to sell you a 1000. They were okay with doing that for me. I told them I wanted a few 'sample' parts before making my purchase decision. They were more than happy to send me 2 in that case.
http://www.alibaba.com/product-detail/I ... 1.2.mXwCW9
The 10-20/piece is at volume discount, the price goes up for just two.