[AdamN]

I think the work is spiky so the quotes are inversely related to how busy the contractor is at that moment (for small shops). Also, there is the supply/demand of the people doing the actual work who are often not employees and may be available or not for that project in that neighborhood.

And then there's the availability of the part/unit which drives price.

[hcknwscommenter]

There's also a weird consolidation going on in what are traditionally mom-and-pop style "trade" industries. E.g., a significant portion of the individual contractor Co. vans you see driving around could be owned (or at least partially owned) by the same private equity outfit. Thus, prices and supply can be "managed" to the detriment of the consumer. I think it will be a few years or possibly a decade before state/local/federal governments catch on to what is happening here.

[sokoloff]

Presumably the bid and level of busy-ness are positively correlated rather than inverse/negatively correlated.