Take a look at Chiff and Fipple, where there are review of different whistles.

Copelands, as far as I know, are just as good as they always were. Mike Copeland is still making them. I have one, and I love it. The only drawback is a D whistle costs $200.

As far as how much they cost, it varies. It looks like there's an extremely good whistle made by John Sindt that costs $65 for a D. I played one once and loved it. I guess how much you pay depends on what sort of sound and appearance you're looking for. As far as cheap whistles go, I like the Generation ones. Still, you have to mess with a bunch of whistles to find one with a sound you like.