Short answer –it varies. The overall cost of a PCI Project (from non-compliant to compliant state) can be anywhere from a few thousand dollars to tens of millions of dollars, depending on the type and size of the business, the number of card transactions, the approach to compliance, the current state of security in the organisation etc.
Some good resources on the topic can be found here:
– http://mspmentor.net/managed-security-services/whats-true-cost-pci-compliance-stillsecure-calculates- – answers
Remember that organisations are required to comply with PCI DSS on an annual basis. It is ongoing, and as such, should be budgeted for on an annual basis, not just a once off project.