I do reuse potting soil for my patio plants - mostly green plants, some flowering perennials. I refurbish the soil every 2 years - remove the plants, toss the soil with well cured compost, add 1/3 fresh potting soil then replant.
I do not reuse soil from pots with diseased plants.
Yes potting soil can be expensive if you buy premium brands with fertilizer and water retention pellets.
I purchase the "plain Jane" store brand. I also look for broken bags. You can save at least 50%, if not more, depending on your negotiating skills.
Do clean and sterilize your pots before planting.