With all of the plants I start, if I was to buy soil mix I for all of it the cost would make a big dent in the pocketbook.
I have somewhat goofy rotation that minimizes how much bagged soil I need to get. Yes, I still need to get a few items. (Keep in mind where I am it is dry... so unless I irrigate a lot I don't have enough materials to create as much compost as I need.)
Aside from the garden, I also plant in big pots as well as a whiskey barrel. Each year I crowd them full and by the end of the season they are pretty much depleted. I snip off the plants (which go to the compost bin) and the roots + spent soil get sent to the worm bins. I leave the worms to work through it for a few weeks before I add scraps for them to munch on. Come early spring I sift the worm bin contents and toss it in a wheelbarrow. I add sand and additional compost that was made from yard scraps, toss in any spent container soil that I didn't have room to toss in the worm bin.. add a touch of bone meal and blood meal... refill containers. The compost and vermicompost act as slow release fertilizers so the only thing I do is every once and awhile water them with VC tea.
I hate buying bagged compost. Most of it is just horrible and more than likely contains an assortment of things I want no where near my garden. Even the steer manure has a ton of uncomposted shredded tree filler. As well if the cattle were offered feedstock that had been sprayed with pesticides/ herbicides.. they have found several chemicals pass through the animal manage to survive composting and are still active enough to mess with your plants when you use it! It defeats the whole purpose of amending with the compost.
I found this link to be very interesting.
A solar oven to pasteurize soil for a seed starting mix. I may just have to add that to my list. I don't exactly need it, but I will think about it. I tend to employ the "only the strong will survive" method. I save seeds and frankly plants that require less coddling is a trait I want. Unsuccessful pots where the seed did not sprout just gets tossed in the worm bin. Not many of those though and of course everything put in the worm bin sprouts!