I don't really want to think about this, but here goes...
1987: A500 £399
1988: 512kb expansion, external floppy drive £200 ish
1989: 20MB Spirit HDA-506 £400
1990: Not too much, suprisingly
1991: Amiga 1500, GVP HC8-2000 with 4mb and 100MB quantum disk £900ish
1992: Picasso II graphics card £250
1993: A3000, ex demo £600
Piccolo SD64 graphics card £290
1995: A4000, 2nd hand £400
So around Three and a half grand. I still made money out of the Amigas though
And that's excluding the collection, but that's peanuts comparatively.