Two years ago I did a study on locally available compost products here in Columbia, Missouri. Tested NPK, trace elements, pH, moisture, and organic matter. The results were not perfectly consistent, but...
Cheap products generally had less organic matter and NPK.
Very expensive products were generally pretty good, but probably not worth the extra cost.
The midrange was a good value. The product I recommended was a Cotton Burr compost, which you may not be able to get in your area.
Finally, the winner in nearly every category was my own backyard compost, made from yard trimmings, kitchen scraps, leaves and grass clippings.Commercial operations don't necessarily use the best ingredients, and sometimes a lot of useless material gets in. Many of the low cost composts and manures actually have very little organic matter in them, and are mostly soil. I've seen bags labelled Compost that are clearly just topsoil. If you need that, to fill a hole or a raised bed, fine, but know what you're getting.
If you're buying, find a torn bag to look at. Do you see clumps or grains of soil? Does it smell bad? Fill of wood chips? Then judge whether it's worth the price.
Store bought compost is OK, but keep in mind all the reasons to make your own.
Happy gardening!
