As chip collectors wiser than I have said, a chip is only worth what a willing seller and an interested buyer agree that it's worth at a given point in time. That being said, here's some historical information to consider when determining this chip's value:
1. Cash-in value: None. The Silverbird went bankrupt quite a few years ago; property resurected as the El Rancho - also closed for a number of years.
2. Supply: the chips from the Silverbird bankruptcy were acquired by a well known dealer, so LOTS of these chips were available on the collector market, even after the place closed.
3. Low value: That same dealer used to advertise that if you sent him $2, he would send his sales list, plus this $1 Silverbird chip. So in that case, the chip's value would have been $2 plus a postage stamp. This offer is no longer available; neither is the dealer.
4. Current dealer value: the convention will be in Las Vegas in 2 weeks, and it's likely that some of the dealers will have this chip in their inventory. If you're in the area, stop by and check out values at the show for a current range of value.
5. Book value: The books differ on approx. value, so who's to say which one is closer to today's market. (By the way, do you know the grading on the example you have?)

Hope some of this info helps.