Last year, before I got the Chapin 24V push sprayer, I went to Tractor Supply and bought the
Fimco 20 gallon 2 nozzle boom sprayer. Assembly is pretty straightforward, and cost was decent. I have very little product left in the bottom of the tank when I'm done spraying, and it uses TeeJet nozzles (with 50 mesh screens) so you have some flexibility when it comes to changing out the type of spray pattern you want to use. Mine uses the FloodJet nozzles, since they're not oriented toward the ground but toward the back of the unit. I do have drippage when I turn off the pump, but that could be eliminated with check valve strainers, or diaphragms.
The only complaints I have are it's a royal PITA to get the pump to prime if it's left to sit for a while, and the portion where the tongue of the trailer attaches to my mower is a very light gauge of steel. I had it filled up and sprayed a few times, and noticed that when I was done spraying, the weight of the liquid being off center of gravity caused the tongue to bend out of a "U" shape. I couldn't adjust that portion of the attachment low enough to level out the Center of Gravity of the trailer, so the weight was sitting a little higher than it should, bearing weight on the tongue. I've seen other trailer designs where this wouldn't be an issue.
While searching for the exact model I had, I see they have a
30 gallon with 3 nozzle boom sprayer available with the same spec pump and they're both $299. Good pressure on the pump, it's got a very long hose if you want to spot spray, and I do like the adjustable pressure regulator on the back.
I'd recommend the Fimco product, and if I needed a replacement part, TSC has everything I would need to rebuild it.