Is he wanting a complete new design, or happy with the cupboards he currently has? If the latter, and the carcasses are still good- a change of doors/handles can be all he needs. We did this on a previous property. It updated the look at a fraction of the cost and people assumed we'd had a complete, new kitchen.
In our current property, we went to all the main kitchen suppliers- howdens, wickes, B&Q etc. Wickes, howdens and some independent places all came to the house to measure and provide advice on using the space we had.
He needs to start with the overall look he wants- modern, shaker, modern shaker, country, rustic etc etc. Also think about what he needs to fit in that space- fridge/freezer or Amercian sized one, dishwasher, microwave, washing machine, bin unit, pull our larder etc. Would he want an island, a peninsular or and island unit on wheels for chopping/storage that could be moved about? There is also the cost of the worktop, and what type/pattern/colour?
We got some ideas from the regular kitchen places, but ended up going with an independent supplier and our carpenter fitted it. The kitchen guy worked from his home, but had access to multiple suppliers/door/carcasses', designs etc. It cost less than the main stores yet the finish is high end.