SP's and v4 block assignments

[andrellio at yahoo.com (Andrew Elliott)]

Hello,

Looking for information on the current standard practices for charging customers 
for larger than default v4 assignments.

Especially with the rapidly depleting v4 space, how are SP's handling these 
requests?  Is it safe to assume customers requesting larger blocks are willing 
to pay a premium?

How much are SP's charging and what are the thresholds?  What are default 
allocations based on?  (ie: size of the circuit, type of product, etc...)

Are SP's requiring more strict justification for said assignments?

Thanks in advance,

-drew