16 Lbs is not much at all. In the post, he explains that it is 1 large and 1 small rock. You are buying used rock of which you do not know the condition, or type, nor the quality of care under which it has been kept. I would recommend against such a purchase. If you are looking to save, you can use some base rock, but again, I would recommend against using lava or tufa rock. Seek out local Reef or Marine Clubs. You can often get well cared for Live Rock for a fraction of the retail cost. as an example, I was sold about 50lbs of premium fiji rock for $75 from a member of the club. I was given about 20 lbs of base rock at no charge from another member, I purchased about 20 lbs from the LFS at $8 per pound, then purchased about 50 lbs of Fiji LR and live base rock for $50 from yet another member of the local club.
You will want about 50lbs for your tank, more if it's poor quality or dense heavy rock.