Not sure about home-made sprayers. Kinda a pig in a poke....depending who built it. Myself....I would have a problem with a towed sprayer like that as my land is too rough.....and I like a sprayer that mounts on the rack of my 4-wheeler.
Lots of guys buy the FIMCO ATV sprayers (12 Volt Pump) and those can have a boom and a hose / gun. I doubt if a new one would cost $100 more. That's the direction I'd take.
Also, have heard some good reports on some sprayers by Northern Tool.