You don't need much for a ground cloth. I think 2.2 oz ripstop is overkill. In my view (others may disagree) a ground cloth serves mostly to keep moist earth from making your bag wet from the underside. So you want something waterproof, not necessarily rip proof.

I'd go with a temporary solution like a thin sheet of plastic. Just use it until it wears out and then get another. Gossamer Gear sells some that are amazingly thin but last for quite a few nights in my experience. I've heard that you can get something just a little thicker at a paint store that is used as a drop cloth. A sheet of Tyvek is another common ground cloth and it might might last longer. Heavier than the plastic but lighter than 2.2 oz I would think.