First Day Of Issue

I have a couple US 5 cents and a gold dollar "first day of issue", complete with sealed envelope, cancelled postage stamp, and, I assume, the documentation. The envelopes are unopened. Obviously, I can get a value for a proof coin, but these are special due to they being some of the very first of their kind to be released.
Any idea how I can value something like this?

Welcome to Numista and best wishes for 2019
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So pictures would be welcome

2000 Sacagawea dollar


2004 5 cents


2005 5 cents

Ebay is a good place to start
gold dollar commemorative set, new five cent coins