I don't know how available it is elsewhere, but around my town there are a couple of places that will do a "full paint job" in a few days, if you can pick a single color, for a couple of hundred bucks.

Fancy stuff, like flames and gliter paint cost extra, of course, but it's actually fairly cheap just to change the color.

If you pick a car that actually has a hood (in front) there are a few places where you can pick up a fancy ornament (steer horns, donkeys, a lion or tiger up on their hind feet - I've even seen one guy with a rather large pink flamingo up front. Usually under $20 (US) and some come with built in lights (eyeballs or other). Try a larger truck stop, since truckers seem to like gaudy, and anything "too big" for your car will make it exceptional.

My old VW beetle sort of stood out because of the trailer balls front and rear. (If you tell people the boat's at home, some will understand.)

A few "bathtub daisies" (stick on anti-slippery pads) strategically splattered on doors and such adds a distinctive touch. Popular on "hippie vans" a few decades ago.

In my area, it's best to omit the "fringe around the windows" and fuzzy dice on the mirror (and some shades of purple paint?), since people might take you for a pimp, but "west coast mirrors" on a really small car will make it stand out from the mundane.

John