It normally costs quite a bit of money to "caption" a video. Richard's friend probably did it pro bono for experience and goodwill, but professional agencies will demand quite a bit of money for their services.
To caption a DVD, one would have to be able to edit the DVD on a DVD program, insert the captions in that format, and then create a new DVD. Again, that costs money. CaptionMAX should be able to give you a quote on that, but again, it's not like it's $15 -- more like $1500.
What you really should do is contact the company that produces those DVDs and complain that they're not Title III compliant.