It's hard to say what it's "worth" anymore, since there's no standard item that's used to value everything. When gold keys were here, it was going for anywhere from 100-120 keys. But now, the best I can say is that it's the second most valuable item in the game behind the stitch hat.
And you're right on the cowboy pants- they're retired. They're fairly desirable, so you may have a bit of trouble trading for one, but it's nothing unattainable.