1998 Washington Mint 1998 Half Pound "Golden Certificate"

A---Welcome to CCF!
B---I don't know if yours has any specific collectibility value, but I can tell you that:
1---My LCS treats those things as generic silver and will buy them for 50 cents per troy ounce less than current silver spot.
2---They don't pay any more for the ones that have some gold plating on them.
3---This is an established, respected, professional LCS--ANA member, US Mint coin dealer, 80 years in business, etc--not one of those WeBuyGold Scavengers.

If you haven't already done so, try finding sold listings for your item in ebay. If you can find that, it'll give you a benchmark for a high retail possible resale value
for your piece, but don't forget to factor the costs of ebay and PayPal fees into your calculation.

If you were to sell it on ebay, expect to receive a couple of bucks per ounce over spot, just like Double F and Den said. As you may have already gathered, what you have isn't official US Mint coinage, regardless of any ostensible similarities that might exist. One telltale sign that one doesn't possess the real McCoy is the lack of any dollar figure assigned to the "coin" (which is really defined as a medallion). The FBI tends to go all black mask and MP5-y when any private mint makes a product that looks a little too much like real coinage. Look up Norfed for a nice pithy cautionary tale on what happens when Uncle Sam decides to throw his weight around a little.