To say that someone is "stingy" in French you can say "avare." "Radin" is less polished than "avare" ^^

In Canada, we had the famous Séraphin Poudrier (a character from a radio show, then tv show, then major hollywood type film) so if you call someone "maudit séraphin" (darn *this guy's name*) you called them the most stingy ever. If you have not seen the film, go and watch it, bring tissues! By the way, the film is actually called Séraphin: un homme et son pécher.

"radin" is the most used word. "avare" is less used though common. If you want use a slang term, you can say "crevard(e)". "File moi 10€ et arrête de faire le crevard" You can also use "rapiat(e)" that is milder than "crevard". You can use the adjective "sale" to be more insulting. "Sale crevard!","Sale rapiat!"