Flint means hard stone. Just imagine Skinflint with a person having hard skin. In Hindi, we used to say, 'Paise dene ke mamle me iski chamdi [skin] moti [hard] hey'. That means unwilling to give or spend.
skin+flint~flintstone a cartoon remember he is wearing skin of animal because he doesnt like to spend money to buy cloth
SKIN + FLINT ... if Flintoff is a MISER then he would become SKINny as he will not eat anything to save money
SKIN+FLINToff feeds on the skin of animal as he is miser n stingy person.
SKINFLINT = using flint(stones for making fire) till it becomes skinny(small). USING EVERY PART IN IT