I know next to nothing about champagne or sparkling wine, but I do know I'd like to have a bottle that costs more than $3.99 for my little gathering. But not much more than that. Luckily, Slashfood has my back. They have rated eight brands of bubbly of varying tastes and low price points, so if you are as clueless as I am, you should find this helpful. They even have a bottle of champagne sparkling wine that tastes decent and costs, yes, $4.
I was born a Salon Delamotte man and I'll die a Salon Delamotte man:
http://www.salondelamotte.com/flash.php?entrer=1&LangueSite=en&PHPSESSID=2d75063f6006595e9e5d44197e6f5998
As for sparkling wine go for a good Cava, Campo Viejo is very reasonable at about £4-£7.
If you're feeling very flush go for Krug or Dom Perignon both are around £100 which for me is too much.