The OED says that “hooptie” is a variation of “hoopie”. The etymology of the latter is unknown, but they say
Perhaps compare the U.S. colloquial phrase to roll (one’s) hoop (now rare) to go away, be off (1899 or earlier; with figurative allusion to the children’s toy.
So it actually may be related to the hoop toy, but not because of its low value.
Both words date to the early days of the existence of automobiles: the first quotation for “hoopie” is from 1915 and the first for “hooptie” is from 1919.