Yes, you can get good bargains on just about any bubbly that wasn't made in a tiny region of france. Spain, California, New York, and South Africa all have good variants.
^Then you've been unlucky. It's possible to get Cava for about £6 a bottle that's better than any champagne I've had up to about £70 a bottle. I admit I have no experience above that price range.
Never tried this..Louis Roederer, Cristal Brut 1990, Millenium 2000, Methuselah (6L) $17,625?? Shocked I am.
Actually, even in very expensive wines they are starting to use plastic corks due to shortage of cork tree's and better results with the plastic.