We do this from time to time. Super easy, and delicious. We like it on caprese salads of tomato, onion and fresh basil.

As far as cost, though, keep in mind that after you've boiled it there is half as much. The bottle of pre-reduced is more expensive because they started with more, so if it's reduced by half it should cost twice as much, plus a little more for the energy used to reduce it.