Molly Quinn's car is a Jaguar XK 150.
The bill at the Belvedere restaurant was $31.82 in 1959 dollars, which is approximately $300 in 2021 dollars, or $75 per person given that they each had the same prix fixe.
The rich girl that Bud is dating is a dead ringer for his sister! In fact, catching the title in progress, one could wonder why he is going with his sister as a date. It is unclear why the production felt the need to cast an actress who could have passed for a clone of the sister. In their scene together, they are very hard to tell apart.
The "outrageously expensive" bill to a fancy restaurant meal for four was only $31 and cents.