dead rocks can turn "live" once the bacteria recolonise it. Dead rocks can also be used as base rocks. as in whether dead rocks are cheaper than live rocks, it depends on the size. some big live rocks can weigh up to 20kg and it cost u $100 per piece. But the bigger the rock, the risk of having pest comes with it.
if u worried abt starting up with dead rocks and having no bacteria to colonise it. Those bacteria can be purchase off the shelves to help u to kick start or u can get some live sand to "seed" ur tank. You dun hv to worry abt algae die off problem, causing massive algae bloom.
Some reefers here uses artificial rocks. Those also dun hv bacteria colonising it.
The main thing is patience. If u can do a proper cycling of tank, ur dead rocks will eventually become live rocks. Otherwise, ur live rocks will die off, giving a rotten egg smell, and u find urself throwing good rocks and money away.