In my experience, a red wine will last between three to five days in the fridge before the flavor starts to drop off. Since you are looking to balance your health and your budget, you do not need to worry about it turning into vinegar after only two days. The oxidation process is what changes the flavor, making it taste a bit flat or sharp, but it takes much longer than a few days to become actual vinegar. If you are worried about the cost, keeping it in the fridge is the best move as the cold slows down the chemical changes. I often do the same with my leftovers to ensure nothing goes to waste. You can definitely have that glass tomorrow night and it will be perfectly fine.