Coil springs

So the MOT threw up advisories for corroded springs on the 4200. Not a fail, but still, as I like to keep the car tip top, am considering changing them anyway (front and rear).
What sort of money do they cost? And should I be looking at aftermarket of some sort, as an improvement? I remember changing the springs on an Alfa ages ago, and it really improved it, even though they werent uprated? Any suggestions welcome. Note: I don't want to make the ride any harsher

Mine were also covered in surface rust, so I just had them blasted and re-powder coated.

I was and still am happy with the ride so didn't see the need for replacements or after market, just wanted no rust.

I also cleaned my springs up and powder coated. That was a few years back probably rusty again!!