In my opinion, the SW in your tank is the lifeblood of your system. You need not go out and get a salt that is really geared to a reef system, but you do want to use a quality salt.
Regretfully, it is not possible to give you "the best most cost effective salt". This is for several reasons. First, in my opinion there has never been a study done on salts that does not contain a lot of flaws, and because of this can't give good results. You might find a few salts at the bottom of the heap you don't want to use, but the "best" is often very subjective.
There are also some personal factors that come into play. For example, if you have a 10 gal nano, you might as well use a high end salt. You will not save much of anything using a cheep salt. On the other hand, if you have a 250 gal tank, a partial water change is going to run through a lot of salt, and going to be costly. You'll need to make trade offs in price verses performance. Also consider how quickly you can get salt in an emergency. If possible, you want a salt your LFS has, and that they sell enough of it to keep the stock turned over. If you want to use a salt that you can only get online, make sure you have enough to make a 100% water change in an emergency.