I'd consider the price difference between replacing the rear mech and cassette, or simply going to an 11-27 (increase of roughly 10% ratio when going from 12t to 11t) and then dropping your tooth count up front.
Have you seen the price of chainsets? You're suggesting new cranks and rings and a new cassette, when for under £50 inc. p&p he could get a Deore RD and HG50 11-34 cassette
Have you seen the price of chainsets? You're suggesting new cranks and rings and a new cassette, when for under £50 inc. p&p he could get a Deore RD and HG50 11-34 cassette