As far as I know, this should mean that he took bids for the job and hired other people to do it for thirty grand. I checked on Google, and which seemed to confirm this understanding. So I understand your puzzlement if the contractor did the work himself.
Maybe someone with contracting or business experience will have a better explanation.
"Now Taylor's place, that was a classic! Bid that job out at thirty grand. Know how much it cost me to build it? Fifteen! Taylors were happy, and you bet I was happy! Hope they never check the insulation under the floor - it isn't there!"
Maybe he had somebody else do the actual work. On his part, he supervised it and bought the material. What do you think?
bid out: To offer (work) for bids from outside contractors.
Yet the context certainly seems to require that we understand it as if he had "bid on" the job. Perhaps this usage is more common than I realized. Possibly the author himself was confused. Desert Cat's advice seems good.
It is possible that the speaker carried out some complicated crooked scheme involving bidding out the job and keeping the money that I can't figure out. The speaker does seem to be crooked. However, this seems less likely.