I've never had a really good Cava. But I have had some decent ones at good restaurants in Spain, and even a few in the Netherlands, where they love Cava. I think the NL must import more Cava than any other country. That said, I rather doubt you will find a good Cava in America.

One of the posts above mentioned small artisan Champagne producers. Here in France I get really good NV Champagne for around 5 bucks a bottle from a producer you have never heard of. And that is only from a friend of a friend.