well a few suggestions and $$ facts:
-dirt cheap auto paint is $40 a gallon
-decent auto paint is $60 to $90 a gallon
-no need to mention PPG and Glasurit, i'm quite certain it's out of your buget
spray guns: house spray guns are not "HVLP" type and are usually half the price. however they also are designed to splatter paint onto walls and stucco, which is way too much for what you need and the results will never dry an look like turds.
option 1:
a cheap compressor is about $50 to $70 and a touch-up or detail spray gun is about $10 at HF. it will not be fast and it's useless for a car, but it will prolly work on a kart frame.
option 2:
harbor freight also sells rechargeable spray cans at $8, you put in paint, close and tighten, then use a car tire pump ($10) to pressurize to what it says in PSI. it lasts a minute or 2 spraying and then needs another minute to recharge. it may spit uneven blobs like rattle cans as it uses the same nozzle.
option 3:
get a "paint sprayer" from harbor freight, its a blue HVLP style sprayer with a hose going to a big fan. it makes half decent pressure and volume and will spit blobs but it's fairly even and i painted a boat and it turned out just fine. i used rustoleum quart of paint, which you can rub off with fingers (aka a waste of time).
option 4:
the obvious one, get a half decent compressor ($100 to $200) and a decent HVLP spray gun ($60 to $100) which will mist the paint on and prevent running. this is the only 'good' way to get results and the only professional way, but its also not the cheap way. if you ever plan to paint automotive stuff, just get this. if not, cheaper alternatives will work for kart frames, the results dont need to be pretty.
i have all of the above. ive tried every one of the methods, only HVLP gun + compressor makes passable car body paint.