Unflavored is very not bad, and I find myself vaping it pretty frequently. You didn't specify, but if you're using 3, 6, 12 or 18mg liquid, you can get it dirt cheap right
HERE (it's even on sale through tomorrow), as long as you're not too picky about PG/VG ratio. If you find it acceptable, you can save even more money buying a high-strength nic base (such as 100mg/mL) and mixing it down to the strength you want (plain PG and VG are widely available, even at the same site I've linked).
You can also use unflavored e-liquid to dilute your sickly-sweet green apple and see if it works better. Try cutting it in half.
On the flip side, if you don't like it unflavored, that site also sells concentrated flavorings. You can get some of that and use it to spike your unflavored liquid a little at a time.