Of course, the Born-Haber cycle is the right way to do the calculation.  Quasi-chemical theory deals with exactly this issue.  You can use the ionization energy of a molecule from, say, B3LYP or CAM-B3LYP (functionals which were parameterized against experimental ionization energies), and get good approximate solvation free energies from a Poisson-Boltzmann calculation using APBS.

A few articles using the method are linked below.

http://pubs.acs.org/doi/abs/10.1021/ct100431m

http://dx.doi.org/10.1016/B978-0-444-59440-2.00004-1

You could also check out this recent review:

Computational electrochemistry: prediction of liquid-phase reduction potentials

http://dx.doi.org/10.1039/c4cp01572j

thank you very much