Having Trouble Finding a Plumber Who Can Do This

We have a pit in our boiler room that houses the trap that sends sewage to the street. It has been drawn to our attention that this pit is only lined with wood, not concrete as it should be. The wood has deteriorated and the earth walls are collapsing into the pit, blocking the pipes. In addition, we have a long history of sewage backups resulting in sewage coming up in a footwell by the back door of our garden apartment. We have been advised that we need the trap pit redug and properly lined with concrete and a new trap. We have also been advised to get an ejection pump that will prevent sewage going to the back of the building. Most of the plumbers we’ve called don’t do it (Balkan, Sewer King), and we’re not sure if we need a plumber or a contractor who also does plumbing. Ace Contracting does it, but their quote was $18K and we’d like to get some other quotes as well. Any recommendations/advice would be greatly appreciated. Thanks!