The market leading low-volume applicator is the DE1008.5 manufactured by Dohrmann Enterprises.
Retail price: $2050 (plus s/h)
These systems very greatly on components and configuration but are designed for the same purpose.
Systems will range in size from 15-100 gallon capacity and include a diaphragm pump and come with 1-3 nozzles. A pressurized system controlled rate by pressure and nozzle size and numbers. These systems can come with optional in-cab rate control adjustment.
Available also are stand alone pumps, for use with existing tank/barrel.
Retail pricing from around: $250-$1500