I'm not sure initial quotes will be the most expensive options. Loft companies tend to quote on a generic design, which includes a set number of light switches, lighting/power points etc. And then there's usually their generic finishes, wall tiles, floor finishes (if provided), paint finishes etc. They maximise their profits by churning out identikit layouts and specs, so if you want anything away from the norm it will be an extra. As Loz points out, get the design right first, this will dictate the final cost. Ensure you're happy with their finishes, e.g. are they allowing for a tiled finish to the bathroom, if so, what do the tiles look like. Will it be fully/half tiled, or just splashbacks. If you want to save some money you can ask them just to provide a 'shell' finish, get your own tiler in, and ask them to finish the ceilings in standard matt emulsion, but leave a mist coat finish on the walls for you to finish off. All in all, just prepare yourself that the quote won't be the finished price...