Fox Farm and other quality organic soils certainly are not cheap. Some others (like Pro-Mix) really aren't actually soils at all, they are entirely soil-less mediums based on sphagnum or coir.
Soil can be recycled indoors and reused indoors. Depending on what kinds of fertilizers/amendments are being used, some can provide nutrition over long periods of time. Bone meal, greensand, and rock phosphate for instance are capable of fertilizing for years. You can basically recook or compost/vermicompost with your used soil. You amend it with more slow release nutrients, maybe add in some red worms and organic matter, keep things moist and very well aerated and wait 30-60 days. Proper aeration is key, and the earthworms can help with this tremendously. If things are not aerated properly then anaerobic conditions will result and anaerobic microbes will proliferate; the mix will start to smell like sewage- it then cannot be used.