Im guessing the darwin and the provari are out of your price range, the next list for price vs quality are going to go like this, and in this order:
Buzz
Lavatube
madvapes vv box
mod.
The lavatube is probably the best cost/quality ratio but it regulates itself. If you toss a low res atty or carto on it its going to drop the voltage down to compensate for the amp draw. Phil put out a review on this less than 24 hours ago and its the most informative in depth review on the pv I have seen to date.
pbusardo's Channel - YouTube
Its a really good device for the money. The vv box mod from madvapes is cheaper and unregulated but dont drop the thing.
There are other VV devices out there obviously, but these are the mostly widely known and used vaporizers. Phil also does a review on the SVR and the ego VV. While they *are* technically variable voltage, you cant fine tune them.