Putting aside most of the issues with the show...why did Rossi call the Bonus Round "the shopping spree of a lifetime" if contestants couldn't buy more than one prize? Several players who had more than enough to buy more than one prize couldn't, and it's not like the "Temptation Dollars" were legit US currency anyway.
No Budget, basically. Yes, "only one prize" was also the case on many other versions of Sale (barring the 1983 Tournament of Champions in America), but in many cases there were prize levels past the car - like, say, the Lot. A few versions did have a car as the final shopping prize (including the 1989 British revival and both of New Zealand's versions), but none of those had an appearance limit either.
The absence of the Lot was made particularly obvious when three champs did so well on Temptation that they reached the car level in just three days (Shiron on February 25, Niki on April 14, Jennifer on April 23)...and that was it. Jennifer seemed to think there was something beyond the car and wanted to keep playing Super Knock-Off, but Rossi had to talk her into stopping.