That could include installation and maybe operating costs. The signs themselves are not particularly expensive, when mass-manufactured, and the prices are falling, with more inexpensive technologies (blame China for the falling prices in cheap LED advertising sign market). One price quote I heard was $8,000 USD, but I had heard it has fallen to $5,000 USD now. Famous Players installed these screens when they were still $20,000 CAD.
Also, Billboard Ethernet Protocols are slowly becoming standardized, to the point where all you need is a $199 walmart computer to operate the captioning.
Hopefully within 10 years it'll be $500 for the sign, plus the usage of the existing computer hardware already in a modern projection booth, utilizing fully industry standardized stuff rather than expensive proprietary-made stuff.
Caption decoders used to cost $500. Now closed captioning costs less than $1.00 per television, because the same computer chip that displays the menus and "VOLUME |||||||||| 100%" bar is used for the captioning too!
A price drop of one order of magnitude will happen (at least for the hardware itself). Give it at least half a decade to a decade, probably sooner.
Of course, installation and operation costs are extra. That will probably fall over time, as things become more and more integrated and standardized. (I remember digital sound used to be incredibly expensive to retrofit in a theater, but prices have fallen over an order of magnitude)
Especially if some kind of mandate eventually makes it captioning a requirement like disability ramps. (And much like FCC mandated captioning being built into all TV's)
Within about 20 years, a 100% penetration rate for big-name multiplexes isn't quite out of the realm of possibility. It's possible. All it may take is a mere 5 million dollar grant by a rich deaf person 10 years from now COMBINED with a mandate, to coax the theaters to install inexpensive mass-produced captioning systems. (No need for the $100+ million donations that routinely happen, like Bill Gates Foundation $150 million to fight AIDS/malaria/tuberculosis)
Besides, some Digital Cinemas today already use encrypted DVD-like discs that can have provisions for a built-in caption track that can be routed to an RWC-style system. Almost all DVD's have builtin subtitles, they just make a future special super-high-def IMAX-quality "DVD" for the movie theaters (There is a 24 megapixel prototype digital cinema projector already! 3840x2160x3chip prototyped by Sony).
Within 20 years, many cinemas will be digital electronic cinemas. When things become standardized (much like today's DVD's with subtitle tracks), it'll be cheap to pipe the caption information to a cheap $500 LED billboard at the rear of the theater using an industry standard Ethernet billboard protocol.
Never say never. It may take 20 years, but 100% penetration of captioning is possible. In about 10 years from now, all it would take is a mere $5 million for enough captioning systems for ALL of North America's mainstream first-run hollywood-film theaters -- provided the cinemas install the captioning systems themselves. (By the way, a SINGLE mega-multiplex cost more than $5 million to build nowadays!)
It will take time... But it will happen. Just 20 years ago, nobody believed that nearly every single television would have a caption decoder!
Example Requirements Going Forward:
1) An industry standardized billboard protocol widely available in advertising billboards (preferably Ethernet based). There's several standards, but some of them are converging into an industry standard. Forget proprietary captioning protocols.
2) Cheap mass manufactured billboards for captions (i.e. China-made advertising billboards). Just use dark glass to dim them for theater use. Though, some models now already have adjustable brightness. Prices will continue to fall over time, until a large LED marquee billboard costs under $500.
3) Industry-standardized closed captioning track built into the movie. This is already becoming more and more common, thanks to RWC/DVS.
4) Inexpensive compact software that translates the closed captioning track for use by billboard, installed on the existing projection-booth computer (computers are quickly becoming standard equipment in many projection booths).
5) Future movie standards such as Digital Cinema, to have specifications for built-in closed captioning that can be cheaply routed to ordinary advertising LED billboards.
As things improve over the years, prices of retrofitting a movie theater for captoining, should fall over an order of magnitude.