Years ago, I bought heavy black velvet finish curtains from a theatrical supply house-I think they were even fire retardant. These were not marketed as acoustic material so the tariff was far less. Don't know if the OP is in a city that has a supply house like this- often, theatrical stuff is sold in the reuse market as well.
Worked great for my needs at the time-- I wanted to black out a large room for use as a home theatre. Looked good too!