Two part anser for you questions:
1. Alcohol vs. windex as an airbrush cleaner for Tamiya acryics--I don't know which is cheaper, but windex does a better job of cleaning an airbrush than does alcohol. The windex dissolves the tamiya acrylic, while the alcohol is just a diluent.
For other brands of acrylic, windex does not work as well. For example, I've tested the cleaning power of windex of tamiya vs vallejo acrylics. Windex clearly dissolves the Tamiya paint much faster than vallejo.
2. Don't use solvents to clean your regular brushes. Just use soap and water. The trick to keeping your brushes clean is to never let paint dry on them. Regularly swish your brushes in water while you are painting. Then when you are done, clean with soap and water. I also like the Master brush cleaner that someone else mentioned.
If you do allow a little paint to dry on the brush, you can try a cleaner like Winsor and Newton brush restorer. But don't soak the brush in a solvent overnight because the bristles will come loose (I had this happen once).