The reason (relating to my other comment) can literally be ‘it is 2022 and these are the new rates.’
Often that’s enough reason.
is there a more lightweight model where for say 10-20% they'll handle searching, billing, rate negotiations, late payments and disputes?
i'm not sure if i'd go into contracting again without something like that. it takes far too much energy to be the asshole that is necessary to not get screwed in business (for yourself) and it detracts from the actual work and life satisfaction in general.
Be matter of fact about new prices, and try to explain as little as possible.
(But always give some reason. Any reason beats no reason, but a simple even vague reason beats too many reasons.)
Baffled me for years until I started to understand that I needed only to offer fewer and simpler reasons to get my ideas implemented.