Translation:Meat is expensive.
*if you don't count all of the subsidies that go to the meat and dairy industry and the animal feed thereof and disregard the price floors put on produce. (That is to say, part of the bill is hidden in your tax returns.) Meat always is more expensive because it takes more to produce. Not only do you have to feed the animals, you have to feed the animals' food, an activity which takes its own time and dedication.
My guess is that it emphasises meat over other foods. '[noun] は [adjective]' can be translated as 'As for [noun], it is [adjective]', whereas '[noun] が [adjective]' is closer to '[noun] is [adjective]'. The first translation sort of implies that some alternative is less expensive.
Luke is right. The diference is the emphasis. Without a context, it's complicated. Both structures can be used, depending on what you want to stress and it depends on the context or the question you were asked. Both "にくは高いです" and "にくが高いです" are acceptable sentences.
にくは高いです is a suitable answer for the question "Is meat cheap or expensive?" because は put the emphasis on what is after it. In this case, the information the person wants to know is wheter it is cheap or expensive. I mean, the answer of this question could be only "It's expensive" (or 高いです), but couldn't be "meat" (にく).
As for にくが高いです, it is a suitable answer for the questions "What is expensive?"* because が put the emphasis on what is before it. I mean, the question establishes something is expensive, so what is really important is the thing that is expensive i.e. meat.
*Before someone says it is an unreal question, it's a perfectly plausible question if you only heard something is expensive, but didn't hear what. It makes in a wider context like. "Rice is cheap in Japan. What is expensive?"