Google is by no means the only metric, but it's a good gage for worth because "Something's worth as much as someone wants to pay for it". However, here's another that I can not discern how this Bag of 40 is different from mine that sold for $49.95? Which are considered more collectible or valuable out of Rainbows, Cat's Eye, Vitro Cat Eyes, and Marine Puries?:
1964 Vintage NOS Marble King Marbles 40 Glass Marbles SEALED Package Milk Glass
https://www.ebay.com/itm/186037315786?_skw=marble+king+marbles+40+ct+original+package&itmmeta=01K07HT5NM0VWQEBXBW4CAFZ6V&hash=item2b50b028ca:g:OwAAAOSwhKtiYC5y&itmprp=enc%3AAQAKAAABAFkggFvd1GGDu0w3yXCmi1dLOtOU9xSw9R17RiBRcPtMJZwQR2%2B%2FChE7KV8pc%2Ba6N152lIQyQdmh8WPZtiWJHRybbnbZKZGVaGR9WyHl%2BEtLJW%2FrYfvFKl7L5OoBufUw0o5KnqAgz0nTbjkEGXdMkYUalqw8YcVC4Av%2BqZUUVIDK4lHPKFSusB7KL9Y1d%2B5%2BMUfIuvtt07F5Q3hx4ON9tL22Sj42CANF5o7FonwP7sw3CuOaRlKuq1gjhCmkhjxL7v4%2FMMeJW1xLvywGlHQ68g5fo5HtjaC8SV2hRmO7aFJXW%2BdFeoKed3VMsjDzibd4FRCJykPF5gimuZoiOBuPETY%3D|tkp%3ABk9SR_ja6PGBZg