There are a lot of factors that go into responding to this question. There are audit, consulting, software, internal resources, and other factors to consider which can easily grow from $30,000 to $200,000 depending on how the effort is accounted for.
We have a SOC 2. How much effort is GDPR?
Assuming your Company is subject to GDPR, the level of effort depends a lot on the maturity of Organizational and Privacy controls. The Organizational will be mostly met by implementation