I know google is like a four letter word around these parts but I use google fi
http://fi.google.com/
Can’t be beat in terms of cost and coverage (in my area) assuming he needs a data plan. the biggest downside is...well... its google :)
You get credits back if you don’t use your full gig and if you go over a gig, you pay by the megabyte (a penny each?) instead of big chunks/bands of data.