Least expensive method is to ...

Least expensive method is to think. #1 all plants need micronutrients. If seasalt/water is 5% by volume or less you are ok. (Do check the ph parameters of crop growing). If water source changes have a routine of checking ph on a regular basis.  If the ph is slightly off then you can select native plants that crave the seasalt more than others. Wild beets for example. Your local county agent can help with this.  As a last resort spend money on a proven technology.  You may want to build up your soil fertility. Healthy soils can handle a ph range of 5.5 10.0 .  Makes the above suggestions less worrysome.