A whole lot more than you even think man! And i am one of em. Ever install a dual stage fogger kit with a WOT switch, purge, remote bottle opener, window switch etc? Ket me know how easy it is to do that!
And most legit kits are not a push of the button. There are progressive NMU’s that distribute the nitrous flow.
And why build a motor for spray? B/c you can have a pretty docile car that you can run a 300+ shot through!