If you want to talk about long term cost, well There are plenty of public school who neglect to teach deaf people because they were meant to use oral only approach. In the long term, Some of them end up in SSI because lack of education. And there's plenty who were success and still costing the govt money for captioning and even interpreting (they learned ASL late in life) . Once you hit adult world, The parents or the gov't isn't going to pay for the service deaf need concerning hearing aids/CI . Deaf people get discriminated base on how well they can hear and some of them get stuck on low paying jobs... hearing devices is costly. not everyone have $8,000-$10,000 hanging around when their warranty run out and they need a replacement. They have their own children to worry about. The sad thing is, if they go on like this, they may lose their speech ability because they can't hear themselves. You may say they can get medicaid to pay for it when they are older, but doesn't that just prove that CI is just as costly as ASL deaf?
I wouldn't be surprised if deaf oral-only use captionist for everything. they definitely will use it in college and courts. I don't think most want to take that risk especially in court.. and I think it is the same cost as ASL deaf (oral only deaf also use captel and tty/ip-relay service)
So to me, they both as just as costly.
But I do want the gov't to show respect for deaf parents (and hearing) if they want to raise their children as deaf and ASL, instead of looking at them from a medical perspective and feel that something need to be done.