The beam itself is rarely the expensive part of removing a load-bearing wall. Most of the cost sits in engineering, temporary support, getting the steel into the room, and putting everything back afterwards. A quote that only prices the steel is not a quote for the job.
Structural calculations
A structural engineer sizes the section for the loads above and specifies bearing, padstones and any connections. Building control will want those calculations, so they belong in the scope from day one.
Temporary support
Before anything is cut, the load above has to be carried. Acrow props, strongboys and needling through the wall are all planned work with a cost and a sequence, not an afterthought.
Access and lifting
Getting a long steel section into a terraced house through a side alley is a very different job from craning one over a detached property. Access dictates section length, whether the beam is split, and how many people are needed on the day.
Fire protection and making good
Steel usually needs encasing or intumescent protection to meet the required fire rating, then boarding, plastering and reinstatement of ceilings, floors and skirtings around the new opening.