You can buy cutting mats reasonably priced with a 40% off coupon at Joanns and frequently they will be on sale and there will also be a additional % off coupon. Also you really do not need a "giant" mat. I have a 12x18 mat wich works just fine and was about $12 after coupon at Joanns. It ia possible to get away with even a smaller mat. A good rule is to buy the biggest mat you can afford.
Using glass- Bad idea!!!!!