This was a very popular souvenir at both parks during the early 70's. Originally it was made by a company called HouzeArt, and they also made a "fluted glass candy dish", coasters and some other trays for both parks, and lots of other tourist places in the US.
A pretty common find at yard sales and usually overpriced at antique shops and collector shows.
The early ones used dark smoke glass and gold leaf accents. The edges of the glass are smooth and there is a dimpled texture to the back. It is my thinking that later these pieces were replaced by contracted pieces made for Disney in SE Asia. Over the years, the quality decreased, the gold leaf was eliminated, the edges became sharper and they went to clear glass. I believe these were no longer sold at the parks by the late 80's.
Although you seem to have one of the early, quality pieces, I am afraid that you will find it does not bring much on eBay currently. Use Advanced search ... Disney World tray... completed items... and you'll see that similar items get no bids at $4.99.
In the box, early version, I would say a value of $10.00- if you find a bidder or collector who does not have one.