'030s are pretty easy over at AmigaKit, very affordable one at only $115 or a nicer one for about twice that:
http://amigakit.leamancomputing.com/catalog/index.php?cPath=43'040s and '060s are much less common, I'd expect in the area of $250-$350 for an '040 Apollo or something like that, and a Blizzard 1260 will probably be in the $400-$500 range (all USD.)
For the money, I'd say the $115 one at AmigaKit would be a good choice, it'll make a very usable machine.
