http://www.forrestrace.com/blue-champagne/

Any recommendations for budget champagne?
Hi
With a wedding rapidly running out of budget – we are looking for a low cost champagne for our toasts. It does have to be champagne and not sparkling wine and we have heard that Tescos Premier Cru is surprisingly good( no sure if it comes with a blue and white striped label though lol!) Any experience or recommendations?
Better to have a good quality sparkling white than a miserably poor champagne.
http://www.marksandspencer.com/gp/search?field-keywords=cava&x=0&y=0&node=42966030&viewID=all-product-search
Cava is made using the champagne method and the bottle above is a remarkably high quality for the price. Providing the bubbles are tiny and plentiful, nobody will spot the difference.
Go get a bottle of this stuff on a Monday and stick it in the fridge – it should be properly chilled by the weekend, when you can try it in champagne flutes. I challenge you to tell the difference
Manhattan Transfer Blue Champagne