[Petroica]

I'm looking at getting a 500mm lens for my D200. I prefer wildlife and bird photography, and have been researching which lens' would best suit within my budget (which sadly does not come near any Nikkor or similar options).
With this in mind I'm looking at the Sigma 170-500 and 50-500 lenses, however my local camera store doesn't stock them so I haven't been able to try them out. I'm going to Kansas City in a few weeks, can anyone recommend a camera store there?
Aside from that any comments re either lens would also be appreciated.
Thanks
Rach