In another time, "estate sprayers" were marketed. 25-50 gallon tank on a trailer, gas driven pump, and ability to fit a boom on the sprayer. Unfortunately, most of the tow behind sprayers have electric pumps and their "booms" are two flood nozzles spaced far apart. I am fond of gas driven pumps for their ability to provide good agitation and have enough pressure/volume to run a boom with AI tips. Not having agitation forces you to fill from a nurse tank with good agitation and worry about keeping the load in suspension while spraying. You said this rig would be used to treat St Augustine, with some zoysia. A lot of what is sprayed on those grasses is not a clear liquid. I treat those grasses too and most of what I am applying is either a DG, WP or a flowable. What I mentioned about the boom fitted to the back of my truck is only for open fields. Most of my properties are extremely cut up or completely inaccessible to vehicles. 300-400 ft of hose and a hand held boom is more manageable.
They who can give up essential liberty to obtain a little temporary safety, deserve neither liberty nor safety.
Benjamin Franklin 1775
Sell not virtue to purchase wealth, nor Liberty to purchase power.
Benjamin Franklin Poor Richard's Almanac1738