Yes, Harrahs did buy the Holiday Casino back in 1992. The overstamped 500 was available in some quantity about 5 years ago. It's currently listed in The Chip Rack, the reference many of us use for Nevada chip identification and values. Value there is $75-100.

Paul might like to add your scan to his valuable web site as well. I don't have his email address but he will probably see your post here. If you like, you could also load your scan to this web site so others may see this chip. Use the FILE UPLOAD feature at the top of this page.