If you're no where near close enough to the action, why would you want a Fish Eye lens? That's a wide angle, not a telephoto, unless you're planning on doing water shots, in which case the fish eye makes perfect sense. K- mount sounds like the old Pentax film cameras. Is this Ricoh a digital, or film camera? The reason I ask is that the new digital cameras also have a need for digital lenses, and old lenses and new cameras aren't always compatible, even if the lens fits. On Nikons, the lens has to have a "D" on it or an "E" for full functionality.
A 400mm Nikon digital telephoto runs around $1,500-$1,700 depending upon where you buy it, Zooms don't usually go that high, and their optics aren't generally as good as a fixed focal length lens. Price them on
http://www.bhphotovideo.com and then shop for a similar lens on eBay to find a used bargain. Unless of course money is no object.