Since this is a custom job, the fabric you use is entirely up to you. Canvas, denim, and twill are options, but they wouldn't be considered 'cheap', unless you get them on sale. My best advice is to go to a fabric store and browse until you find something you like. Since you only need a couple yards, check the discounted and closeout sections of the stores. There, you can usually find leftover remnants a little cheaper than what they normally sell for. You should be able to find something you like for about $5-8 a yard.
And don't be afraid to ask the store staff for help. They can point you to some good bottom-weight fabrics as well. If they ask, just tell them you're putting together a Halloween costume.