Their dev estimated that he’d only need a few days to complete the switch, and it would accelerate the rest of the project.

This is bad.. If your time and planning management is this bad then you shouldn't be in a position to give estimates directly to clients.

It sounds like this project may have been offloaded to other Devs a few times as it was a less priority so some ramp up time for each new handover.

The site looks good but 45k is wild to me.