Normally, the sum of parts should be higher than the price of the total machine. And I said he wouldn't be too bad off if he could fetch it at 200 euro ;-).
One must keep in mind the circumstances the seller is in as well as how badly does he / she needs money. Also, has it been in storage for a long time and if it's a deal between friends. Sure, on eBay stuff goes at outrageous prices but the difference here is that the guy is being offered this system. What I did not know then, but know now, is that it isn'nt in it's original case. I was already wondering how on earth all those drives would fit into a Desktop :-). I agree on the point that the drives won't break the bank atm. He might even consider throwing out all and replace it by a flash-disk-IDE solution.
No matter what... when it comes to Amiga I think two things determine the price:
1) How badly does the buyer want the system?
2) How badly does the seller want to part with the system?
Then all that's left is the space in the bank-account of the buyer to get 1 and 2 to meet :-)