How do I replace the SD card reader on Nikon D5000?

When putting in an SD card, it does not engage and remain in the slot but springs back out. I can see a blue piece of plastic at the bottom of the slot which i cannot remove. it is suspiciously the same colour as an SD card and I suspect a piece has come off and lodged in preventing it from locking in.

Camera repair company say that the blue plastic is something from within the camera but looking at the D5100 stripdown page, there is no blue plastic in sight. They advise that it needs a new card reader and have quoted close to $200 for the job. I'm sure I am being ripped and would like to know how much to expect for a card reader replacement. I am happy to pay for a repair so if you can recommend anyone in London, England, let me know.

thanks