An Amiga 500 was around $600. (edit: $700) A Sun 3 color workstation could easily be $20,000 or more.[1] In today's money that Sun would be more like $40,000.

Also, I don't believe you're correct about the memory being non-upgradable. A cursory Googling suggests at least 8MB could be added, maybe more.

[1]http://textfiles.com/bitsavers/pdf/sun/Sun_Price_List_Dec88....