Outcome:
Trey, next time you are in Houston (or I come up your way), I owe you a dinner.
Given the numerous low cost alternatives to acquire an image similar to mine, I felt that $50 was actually a fair asking price. I also included your FotoQuote range, just to emphasize that $50 should be quite reasonable. They consulted their website designer and agreed that
they could not offer a penny over $300! 
Hmm... I can't figure out if they read my entire email, or stopped at the $600 for 6 month line.

After much deliberation & soul searching, I finally agreed.
Next time I get a such a request, I will immediately buy a copy of FotoQuote.
It does pay for itself rather quickly!
So thanks again for taking the time to respond and be sure to collect on that dinner offer.
We have quite a variety of restauraunts in Houston: .... McDonalds, Burger King.......
