When we lived in the city I would buy expensive paint brushes and clean them really well after every use. You can make good paint brush last a long time. However, when living off-grid it is really hard to clean a paint brush without lots of running water. Now I buy cheap brushes from one of the dollar stores (I think brushes from Family Dollar are better). To make your brush last, clean it to get most of the paint out then dip the brush in a can of water until the next time you need it. Your brush will last for months. If you have a paint brush used for oil base paint, clean the brush, and store it in mineral spirits.
For those of you with electricity and running water, clean your brush really well, rub a little dish soap into the bristles, shape the brush, and let it dry. This can make your expensive brush last a long time. If you have oil base paint and need it for a day or two. Wrap the brush in a wet paper towel and place it in the freezer. The brush will last until you can clean the brush properly.
Cheers and thanks for your up-vote, Tim and Joann