Then they are surprised when they find themselves desperately needing the skill set once the business has decided to do a big salesforce thing and not having anyone on hand who a) can do apex / knows salesforce or b) is willing to do it.
So they often turn to salesforce speciality agencies and pay through the nose.
To answer your question - I’ve seen salesforce agencies bill their developers and designers at a blended rate of $170-$200 for $1M+ projects for onshore (US) talent. I suspect if you are a decent software engineer who knows salesforce well you can probably find clients willing to pay higher rates.