I got sick of paying such a lot for potting mix a while back and bought some of a cheapo brand that was at Lowe's. In the long run, I'm now sure it cost me more than the good stuff would have because everything I potted in it died. Guess I should have known because of how heavy the bag was, there was too much sand in it, and not nearly enough good stuff. It compacted immediately. Anyway, now I do buy the "good stuff" - it says it's all organic which means it's probably too moisture retentive - and stock up when it's on sale. I always lighten it up some by adding Perlite too, but that doesn't really save any money because Perlite isn't cheap either.
Btw, if you buy bags that have been torn and are leaking at Lowe's they sometimes mark them down for you. (I carry an old towel in the back of my car to put plants and leaky bags of soil on . .. just shake it out into the garden when you get home to clean up)
My method for getting the right density in the pot is to pour potting mix in the pot, water it and let it drain. Add the plant, pour more potting mix around the plant, water it again and let it drain. Keep adding potting mix until it's at the right level for the plant, watering and letting it drain. I don't ever tamp or firm the soil by hand any more. Too variable.
