The $60 Battery Foamer — IK Foam Pro 2+ and a Cordless Tire Inflator
Skip the hand pumping without buying a dedicated battery foamer. The Foam Pro 2+ has a Schrader valve; a tire inflator you probably already want does the rest.
Battery-powered foamers are a growing category, and the good ones are genuinely nice to use. They also cost $100 to $150, have non-replaceable batteries, and become bricks when the electronics fail. There's a cheaper route that gets you the same spray head and most of the convenience.
The parts
The IK Foam Pro 2+ is the standard IK handheld foamer with one addition: a Schrader valve on the tank, the same valve that's on a car tire. That's the entire difference from the plain Foam Pro 2. It still hand pumps; the valve just gives you a second way to put air in.
The second part is any cordless tire inflator with a screw-on Schrader chuck and a manual pressure target — the Xiaomi Portable Electric Air Compressor 2 is a popular one, but any of that class works. Many people already keep one in the trunk.
The build
There isn't much of one. Screw the inflator's chuck onto the sprayer's valve, set the inflator to about 40 psi in manual mode, and press start. It fills the air space in a few seconds and stops. If you want it hands-free, a strip of Velcro on the side of the tank holds a small inflator in place while you spray. That's it.
Two details that matter. Set the target to around 40 psi, not the "car" preset and not "max"; the sprayer's relief valve is a safety ceiling around 3 bar, not something you should aim for. And because the inflator refills the air void so easily, you don't need to leave half the tank empty the way hand-pumpers do; fill to the useful-capacity line (about 1.25 liters) and just top off the air when the mist weakens.
What it costs and what you give up
The Foam Pro 2+ runs a bit more than the plain model; a good inflator is $40 to $60 and useful on its own. Compared with a $120 dedicated battery foamer, you save money, get an identical spray head, and keep a sprayer that still works if the inflator dies. What you give up is auto-restart: a dedicated unit turns itself back on when pressure drops, while here you press a button once or twice per car. For a rinseless pre-spray that's a non-issue.
Do you even need it?
If you're only misting rinseless on one car, hand pumping is 15 to 20 strokes and one top-off; the inflator is a convenience, not a necessity. It earns its keep when you're foaming pre-wash at a bay, doing wheels and body, or doing more than one car. If you already own an inflator, the 2+ premium is small and worth it. If you'd be buying the inflator only for the sprayer, buy the plain Foam Pro 2 and pump.
Have a hose? The same sprayer is still the right tool for pre-wash and rinseless; the hose just replaces the trip to the bay for the rinse.