If you're thinking about Acoustic Panels, you should consider making them yourself. The Rockwool Comfortboard 80 from Home Depot is as good as anything out there and it's only $58 for 6 pieces. It's very rigid, so you don't need to treat it at all. Check out the Acoustical Performance here -
https://www.rockwool.com/products/comfortboard-80/?selectedCat=comfortboard%E2%84%A2%2080%20downloads#Specifications&SizesFor Bass Traps, just double up with 2 pieces for 3".
All you need to do is build a wooded frame, add the Comfortboard 80, and staple some Guildford of Maine FR701 cloth on it (about 5yds), which you can order from Duvaltex in Quebec. I added Cambric dust collection fabric to keep any loose particles intact, which is very cheap to buy (use 3M 77 spray adhesive to glue it on over the Comfortboard 80). Anything you buy won't be better than making your own.