We've just done this. Our builder charged £860+vat for labour. We had a structural engineer in to do the plans and that was £450incl. The supporting beam was £220, and building regs were about £350.
About 2k all in, I suppose - the only figure I'm not sure on is the builder's because he actually quoted to do all the work (complete kitchen refit as well), and I had to ask him for a separate quote to do the wall for our building regs application - the cost of the application is on a sliding scale and I wasn't about to pay the fee on all the works we were having carried out!