good inexpensive champagne

[wdonovan]

I would get Champagne rather than the other choices. There's not much available at price levels above but if you can get Francois Montand NV Brut (I believe it's a Blanc de Blanc), you'll be amazed. If I tasted it blindly, I'd guess it to be a $30 Champagne (but it's around $10). It's a staple in our house.
There is however, one other factor here...... your guests! Do they for most part appreciate actual Champagne? It is much drier than the stuff that is served at most weddings. I speculate that people who do not drink Champagne except at weddings think it is a sweet bubbly beverage. That would be their only reference. So...... it's really your call based on this. Do you want to serve real Champagne or would the guest prefer something sweet like they may be used to? If the latter, I'd serve something like Asti Spumante (just don't invite me). I would never consider Cava though because the Cavas I've had were even drier than Champagne. I think you'd narrow the size of the appreciative audience if serving this.