From what I can gather 99.9% of people simply discard any soil which has been previously used once the grow is complete. Basically use new soil each and every time around
Depends on so many factors... If you're just using it, as is, not feeding it or amending it. One and done in my experience. But, if you amend it between grows with some good compost, maybe some worm castings, and you regularly apply an AACT and Botanical Tea then you can probably stretch 3 or 4 grows out of the same base mixture.
Since it's recommended to use new soil each grow, what cheaper priced soils are still quality to use?
Read InTheGarden's post in this thread. It's a bulls-eye. Just get a big bag of potting soil and the other ingredients and mix your own in a big tub. There's at least one thing in this hobby that doesn't cost an arm and a leg.
have you ever seen anybody shoveling out an outdoor veg garden? No, they add new compost and ferts every year to the same soil making it dark and rich, perfect soil. You can take your old indoor soil, dump it into a pile and mix in all you need for the upcoming season. you can always add new FF to the mix if you want