Losing box room to put staircase up to loft?

[Cheeseislife]

So you have a box room at the front of the house, same width as the hallway and underneath that room is the stairs/ front door. How much have people paid to get that room made as a staircase up parallel with the original stairs please? Viewed a house today with an awful ladder up but the room itself in the loft is usable, just trying to figure out if it's worth losing the box room to gain the loft room as that ladder would HAVE to go!

Could you put the stairs in and build the space as kind of a walk through office/storage/desk/shelves type thing under the new staircase against the wall? I'd be happy with that and the proper extra room access.

What's the floor plan like? Is there another room space can be stolen from? We had a very big master that we stole space from instead and kept the third room as a study.
If it's really a tiny box room though you may as well use it for stairs.

Our staircase alone was £600 so I imagine with all the other work involved it would be at least 4/5k but you'd need to look at head height too for building regs.