There's tons of good, cheap options out there. But, my go-to for bubbles is Spanish cava. Enjoyable bottles can be had for a small fraction of Champagne. I'll happily guzzle Cristalino or Segura Viudas, which can be found darn near anywhere, for around $7. If you want to go completely fucking nuts and throw those quarters in the air like you just don't care, you can pick up Avinyo for a rap superstar price of $12, but it's unnecessary and just gratuitous to throw your wealth around like that.