As others have said, quilting can be done much more quickly on a longarm than on a DSM, so it would be unlikely that someone quilting on a DSM would or could charge less than someone quilting on a longarm. I've heard that some people have been able to trade unfinished tops for quilting services, but finding someone willing to do that could be difficult. Some people just enjoy making tops and don't really care about turning them into quilts. If that's your mother's passion, then she might be able to sell the tops on eBay or etsy and not feel bad that they are sitting around unquilted. Or she could donate them to a guild to be quilted and donated as comfort quilts.