I like this Name.
First of all “St” instead of “Saint” is not a problem at all.
In fact, there are more exact monthly searches for “St tropez” than “Saint Tropez” (74.000 VS 60.000)
2) St Tropez is a place for High Society and Artists, etc.
That adds value to a Geo Name.
3) I couldn't find any relevant .org sales in the past.
One was SaintMoritz.net (sold $1800) 2008
4) Anyway, i personally would actively market this name to possible rich endusers in St Tropez (i wouldn't sell this to domainers or just park it, etc.). Luxury Hotels , Property Market , Travel business, etc. -> all possible buyers!
And my appraisal for endusers would be somewhere in the x.xxx range.
.org could be a little barrier, as it is more suited for health/Legal/medical/charity/educational/informational/etc. domain names. but it all depends how you market it. - .org can be marketed as a sign of trust and security.
good luck!