It all depends upon the density, and the thickness.
I'm about to build absorption panels and I did look at tontine acoustisorb (as it was hard to find rockwool for good prices) - since found good density rockwool at a fair price.

Anyway - the best price I found for the acoustisorb was here:
http://www.insulationsuperstore.com/...art/Itemid,64/

The company that i'm likely to go with for my rockwool, though, is fminsulation.com.au - a touch cheaper for me and also higher density. I'll be building a different product though, as that's defined in part by the size of the sheets, and also by the density difference (60kg/m3 rockwool vs 48kg/m3 tontine). My corner traps are now going to only be 60cm wide, rather than the 80cm i'd planned with the tontine, and they're not going to be quite as thick)

Obvious plusses for the tontine are the fact that you don't need to wear protective gear when handling it and don't have formaldehyde as a possible poison.

Also, OC705 isn't all it's cracked up to be - the money range is between 40kg/m3 and 80kg/m3 - much denser and you start reflecting a little bit.
Also, absorption of bass frequencies happens much more when you have thicker units (100-150mm is the most cost efficient here) and when placed over a corner.