Weve gone through this same exercise/question. SOME types of wood bedding can be problematic for Cavies, others less so. We use a mixture of paper and wood, seems to work well with both our American Shorthair and Abyssinian. With regard to cost, yes all disposable bedding will run up your costs. Two possible solutions: First, if you can buy large volume bedding wholesale and have it shipped, you could probably reduce costs a lot. My employer does this for their Cavie colonies. Alternatively, my daughter has been urging us to switch to washable fleece bedding. One time cost, but youll have to run that filthy thing through your washer dryer OR do it by hand in a basin/bucket.
Whatever your bedding changing schedule is, you can usually get some more mileage out of it, by only spot cleaning (and adding a top layer of fresh bedding) once in a while.
Good luck.