Fixed-price ISO consultant quoted us 3x more than hourly

We’re getting quotes for external support on our ISO 27001 renewal across our three offices and the difference between consultants is honestly baffling me.

One firm quoted a fixed package - sounds clean on paper but it’s nearly 3x what two hourly-rate consultants quoted for what looks like the same scope. The fixed-price firm keeps saying ‘no surprises’ but I’ve worked with hourly consultants before who came in under estimate.

My GM wants the fixed price because it’s ‘easier to budget’ but I feel like we’re just paying for their risk buffer.

Anyone in a similar multi-site setup dealt with this? Curious whether the peace of mind is actually worth it or if I’m about to win this argument with my GM.