There are cash machines and they seem to give the best rate. We just took £50 in levs with us to tide us over the first day and £150 sterling and exchanged in the hotel or with our instructor, the rest we got from the cash machine.
I believe the cash machine in the Mourgavets gives a rate of about 2.7 lev to pound. Take pound sterling as well, but make sure notes are new, not ripped in any way and with no marks(i.e pen etc) on them.