Call a local wine store and get a 1 or 2 bottle styrofoam shipper. You'll probably need one sized for magnum bottles because Champagne bottles are usually bigger in diameter. Wrap the bottle in bubble wrap if it's too loose in the shipper. Pack the shipper in your checked bag and everything should be fine.

Champagne is shipped by air in these types of containers all the time. Packing it in your luggage makes it even more secure. If you're nervous, put the shipper in a large trash bag and tape it closed, just in case of breakage.

TSA will likely open your bag and check the bottles more closely, but there's nothing wrong with checking wine or Champagne.

I don't know if there are any issues bringing wine/Champagne into Indonesia.