I've recently fitted a new kitchen where I sourced all the components from different suppliers. It cost about £650 and Howdens quoted me £1100.
There are lots of suppliers on ebay which is worth a look.
friend of mine bought a kitchen from one of the 'bay suppliers - was a complete mess.
Appeared to be all the "2nds" -
holes missing from shelf supports.
Hinge recesses missing
cabinets off square
plastic coatings not glued to MDF core
absolute NIGHTMARE to fit.
cost her about 1k instead of 4k, but at least an extra 40 hours labour.
worth it in monetary terms, but it will never be perfect, and parts of it jar every time I see them - doors that will NEVER fit straight, cabinets that hang not quite plumb. Slight colour imperfections.
Extra holes showing where not wanted.
Would have been less work, and look better, to have them custom built from 13-ply furniture grade birch plyboard, and spray painted.