Wouldn't acoustic ceiling tiles work to some degree or another? (At least mid-highs) It's readily available at most any building supply stores and cheap!

4 simple steps to easy sound control...

1. Acoustic ceiling tiles
2. Burlap - cut to size, color of your choice!
3. Glued down (lightly) face/sides only ...enough to not show the back
4. Attach to wall/ceiling with slight standoff for most efficiency
Can also be cut and finished to custom sizes/shapes!

I moved this post from the "sticky" because you asked a question rather than provide a local source.

Acoustic ceiling tiles do absorb, but they're not generally as effective as rigid fiberglass or mineral wool for a variety of reasons. If you read the Forum FAQ linked in the READ THIS FIRST post you'll see the best way to make absorber panels using those materials.

--Ethan