500mm f4.5 pentax and the NEX7 anyone?

I have a chance to buy this Pentax SMC 500mm lens for about 350 USD?

Anyone ever used it on the NEX?

Any suggestions for a good quality adapter ?

The lens has a K fitting.

(there are many on Ebay for around 11 USD, but are they good enough?)

thanks a lot for a helping answer.

Peter