I put a small piece of bubble wrap over the front of the card. I only use an ordinary envelope, hand made if I need to, the card is made to fit the envelope. The cost of postage is based more on depth and large letter rate is normally ample for a greeting card. And when it's a special card I'm happy to pay what it takes to be able to post it. I also get asked to make cards for people so others must also be happy to pay the postage.