CD dost:
Again, it depends on the composition and the grade the balls are meant to be.
e.g. Kooka 2 piece balls (like kooka Practice or kooka Zenith or kooka reader) will not damage bats.
whereas even Slaz 4 piece might be bat damaging.
Cost gives a fairly good indicator of the ball.
Also, companies like Gray Nics and Slaz dont make their balls- they get them done for cheap from india or pak. Even for India and Pak standards they buy the cheapest middle range so one can imagine the quality of the ball.
Depends mostly on the core of the ball- if its hard goli inside - it will damage bats. leather makes a difference as well but more on the durability rather than the damage caused.
With SG as well- the lower grade balls are bat damaging rocks e.g.SG Seamer and bouncer are terrible balls- rock hard POS. whereas the higher grade balls are good enough for international level cricket.
In fact the SG test ball was the actual ball being used in tests in India. I used to have one ( was a hand me down from a senior player) and that ball didnt get destroyed even after 110-120 overs that we could ball in the nets!! Not sure what the quality is like these days but they will surely not be bat breakers.
pic of that ball below:
http://ecx.images-amazon.com/images/I/41Y9e7xOPBL._SL500_AA300_.jpg
Used to be 500-700 indian rupees which used to be a big deal when I used to play. Cheaper balls used to cost Rs 50-60.
Watch out for cheap fakes as well.
The real SG test that I had was soft leather even after it was worn out.
SG Seam was hand stitched (nice thick thread) and was real easy to grip as a spinner. No wonder Harbhajan singh was having problems once he came to Australia- in Australia they were using Kookaburra for tests and kookas have machine stitching which is not as easy to grip.
Now a days even kids in India/Pak have seen kooka balls! For the last generation it was a distant dream ....(even Ranji spinners struggled once they came on international stage)