As far as the flavor is concerned, I have not personally tasted a noticable difference in flavor in the strength liquids that I mix, where I can say for sure this one "tastes" like it has more nicotine than another. My range is generally between 8-20mg (flavored), and I have vaped unflavored 24mg all by itself to test the strength.
The unflavored to me tastes extremely bland, I can't really put any particular flavor on it whatsoever.
Mixing without nic liquid is the cheapest way that you're going to experiement, as was suggested by Kate51.
Keep in mind your e-liquid may contain a certain % of Glycerol in it, which is not PG, so there may be a slight flavor change when you actually mix your "real" batch. You can supplement that % of the "fake nic-liquid" with VG and you should get similar results. If you are inclined to go that far with it
Best of luck, let us know how it goes!