We present a formalism for determining the cross section for exclusive heavy vector meson production (J/ψ,Υ) as a function of rapidity, in both high-energy proton-proton and proton-heavy ion collisions, at next-to-leading order in QCD. We compare and contrast the production in pp and p-Pb collisions and show how data for these processes can give information on the low-x gluon distribution of the proton and heavy ions at a range of different scales.