I used this type of insulation in a semi self build recently, and found it to be a little expensive alright, but am glad I used it now.
I tried looking into other alternative materials, but couldn't get the necessary info before I had to decide.
There were two suppliers of the sheepswool that I was in touch with, sheepswoolinsulation and ochre wool teo. the latter seemed cheaper, and came in bales as oppossed to rolls, but I ended up purchasing from the former, again because I just had to, if you know what I mean.
If you're putting it in yourself, its a breeze compared to rock wool, its pretty good at what its meant for, and its sustainable too.
Still have a bit to roll out, but all in good time I say.
Have you looked into the blown insulation material made from recycled paper, had it recommended to me on a couple of occassions, and sems worth looking into. Only drawback is that its loose and therefore wouldn't be suitable for spaces you might be in and out of.
Good luck with it anyroad.