Raphaël,
The dreaded "how much" question...
The answer is: it depends.
First, on how much it is worth to you. I have seen things sell for amounts of money i thought were way too high. On the other hand, i have bought stuff myself for amounts other people might think ridiculous.
Sandro's 500 C/M will be worth more than a regular 500 C/M to some people, because of it being the 50th anniversary edition (which, by the way, were not a limited edition, so no 'rarity-value'). Others may not care about "special editions", and do not want to pay more for this camera than they would for any other 500 C/M in similar condition.
Second, it depends on condition.
A beaten and bruised camera, lens or back, or a well preserved s&le of the same will of course not cost the same.
Third, it depends on type/version.
You mention an 80 mm lens, and the bayonet 60.
There are three versions 80 mm lens (C, CF, CFE) you could use, the first version coming in two sub-versions (T and T*). Of these three, there are two (CF, CFE) with bayonet 60 front mount.
Assuming similar condition (very hard, considering that there may be an almost 50 year age difference between the first and the current version 80 mm lens), prices will vary a lot because of the different versions alone.
Fourth, it depends on the market.
The best way to find out what a good price would be is by shopping around, comparing prices.
That last thing (shop around) is what you need to do. See what the things you want go for regularly. Then see if you can find a bargain. If not, be prepared to buy for the 'regular' price.