The Colt Mustang was made in several styles.
In general they go for $400 to $500 depending on condition and style. Lightweight Pocketlites ones in like new condition bring more towards the $500 range with original box and magazines etc.
Note to adriangordon:
Generally posters do not list the full serial number on a public forum to prevent problems of someone with bad intent claiming it was stolen from him and so on.