Consultants! How do you estimate complexity and price of building solutions with workflows and forms?

I search "estimating" to see what would come up in hopes of seeing examples of how other consultants go about this. I find it incredibly complex. Clients generally want a "ballpark" and that's almost impossible to do without a full requirements gathering session. The complexity of certain workflow or form logic / requirements can increase the time and thus the cost, though it may seem like a simple ask to those who don't know what it takes to do it..