If you look at
this page, you can see a graph showing the relative approximate speeds of the various 68k processors available for the Amiga. A 50Mhz '060 is about 5 times faster than the 030 at the same clock speed.
Although it has a 100Mhz '060 listed, I don't think these are readily avaialable. The fastest '060 I've heard of in an Amiga is 80Mhz.
As for prices, look at
www.vesalia.de. Or, second-hand, I guess you could pay about £30 for a '030 card, £60 for an '040, or £100 for an '060.
