OK ......... diamond cutter for the concrete, a 300mm wide trench for a 100mm wide wall.
"Trench fill"... ie fill with concrete back up to ground level. Build brick wall over. You may want to render internally. Modern bricks usually can't be "faced" on both sides.................... or, use a 225mm wall, faced both sides. (Same footings)
Keeping it simple. Maybe one guy working on his own, or possibly with a labourer............. with good access, and somewhere to tip the spoil, then around £2,500 should do it.