I think a IIfx is a very worthy addition to a collection, and one I am saving up for as well.  It is the last of the big box desktops, and (if we don't include Quadra 700 in the cx series case) the most powerful in the series.  Plus you get that super sexy dual floppy staring right at you.  It has some nuances that make maintenance harder, like the 64-pin SIMMs, and the special unobtainium SCSI terminators.   Recent sold units on eBay have fetched between 150 and 700 dollars. Depending on the condition of the IIfx, and any accessories included,  I might entertain a 320 price point for a really good example, but would really look for something under 200.