The parts for these cars are relatively cheap, but not all on 100HP as some are unique,
100hp front suspension parts are supposed to be different, and much more expensive
People have been known to use standard parts from a 1.2, as they fit. But that's not how FIAT designed them.
Some "upgrade" suspension parts improve handling, some make it worse. Some make it so uncomfortable to drive that it defeats the point of having a 100hp in the first place.
100hp wheels are prone to minor buckling, usually on the inside. Causes vibration, and sometimes slow punctures, often randomly. Replacement originals are rare and are usually as bad. Not many aftermarket wheels are correct size and offset.
100hp tailgate glass is different, and some glass companies seem to struggle to get them.
But front bumpers seem to be the absolute worst... and it's rare to find a 100hp which hasn't either got a damaged one or has paint flaking problems from an aftermarket one.
I had to buy a whole car to get an undamaged original front bumper for a customer.
Aftermarket ones can sometimes be got, but they are not good quality and are made of a different plastic which is hard to get paint to stick to, almost impossible to repair if damaged.
(I have a 100hp with perfect sills, good unbent original wheels, original rear beam in really good condition, correct original spec suspension, and an original undamaged front bumper.
Unfortunately it's a red one, and the paint is atrocious (fading, lacquer peel, etc.), and therefore is fairly worthless for resale. On the other hand, it's still a hoot to drive on country lanes. And as its not really worth much I don't feel guilty about keeping it as a toy.)