Put it on eBay and advertise it on all of the AmigaOS4.x related forums and you will likely get the best price for it. MorphOS3.x users have faster and cheaper options, but the options for AmigaOS4.x users are not available at such low prices, or widespread availability as a used PPC Mac computer. Also, for all of your other computer, or Amiga related games, manuals, etc., eBay will get you the most money.

Sorry to hear about your wife and good luck with your sale.