Cinquecento ones? Fitting isn't the point, really, the suspension is what keeps the tyres in contact with the road and makes it controleable.
No idea what you're looking at, but generally you get what you pay for, thusly, cheap = carp, cheap coilover = double carp.
Assuming you're after handling rather than pose, then a set up which works well and will handle in excess of 115bhp is 55/35 Eibach springs, Monroe reflex dampers.