Thank everyone. 55-300 it is. My mind, but more importantly, my wallet is at ease.

I am new to the art of photography and have had a K-x for around 6 months now. Looking to get a Pentax 50-200mm f4-5.6 SMC DA ED Lens telephoto lens for wildlife photography. I am looking at the following teleconverter and can't find out if I will retain autofocus.:

http://cgi.ebay.co.uk/Pentax-AF-K-Fit-2x-Tele-Converter-K7-K20D-KX-K10D-etc-/180... or not?

Any help will be really appreciated as I am on a very limited budget.