I wouldn't recommend using mush. compost. There is a reason that it is only 1$ a bag, it's because it is shitty. What it is, is normal compost that has been used to grow mushrooms in and therefore a lot of the nutrients have been used up by the mushrooms. And they sell it because it isn't good enough to grow mushrooms in anymore. If it isn't good enough for mushrooms is it good enough for your plants. i hope not.

Worm castings are the best but are also very expensive. I use “black gold” it is a mix between worm castings and some other things. It is about 5$ for 8L which is a lot. With soil you really get what you pay for.

Hope this helps