Being in the position I was in (working in my spare time at Microdirect in Manchester) I could usually buy the PC parts for a fraction of the cost of the Amiga hardware being swapped.
The best swap I ever got (Amiga 4 PC wise) was for four sticks of 64Mbyte SDR SDRAM which had been fished out of the returns bin at work for being incompatible / dud.
I turned up with 40 or more sticks and went through them until we found four that worked with his motherboard. He ran them for a week with no problem and I earned myself a nice A4000D.
They were on sale for about £40 each at the time, so the guy might have thought he'd got a good deal, but even if I had needed to buy them the price was about £10 each to staff. (A year later and EDO was gone and SDRAM RAM prices went through the floor and there was no margin on RAM ever again while I was there)