Amiga stuff has always been expensive. The first 030 card I owned (and incidentally the last one), I bought a 4mb SIMM for. Called an Amiga retailer listed in the back of AmigaWorld magazine (boy that brings back the memories) and they wanted $289 for it.
Called a PC vendor here in town, out the door for $179.
Same deal with the hard drive for that same system. 60mb drive from an Amiga dealer (different one)? $149. Bought from a vendor in Computer Shopper for $99.
In this particular case it is, however, economics of scale. They produce Sam boards in bunches of what, 75 to 100? At most?
Compare that with, say, an Asus intel mobo produced in the hundreds of thousands if not millions. Volume discounts!