Ian - Most of the misunderstandings in this thread would have been avoided had you mentioned, within your original posting, that your friends requirements for a "cheap" lens were driven by your reasons stated as above. A simple "He's got a budget of a maximum of £100, and he's not actually a hobbyist 'tog - just want's it to take general snaps" would have sufficed.
The question regarding the PM you recieved was, as stated by others, purely and simply to be sure that no attempt at out of Classifieds trading was taking place, and in response to a number of RTM's we had recieved on the matter.
FWIW, you did get some very good advice, some of which, due to lack of information given by your good self, was not helpful in this case, though accurate nonetheless. It is true that it's a shame to waste the abilities of the full frame 5D by putting a bottle-bottom on the front of it. With a budget figure of £100 tops in mind, I would honestly only really recommend the nifty fifty, or if you're very lucky to drop on one, a 28-105 f3.5-5.5 USM. However, as you know after owning the 5D, full frame Canon's are just destined to be with L glass, and I still reckon that the F4 L's are a bit of a bargain for what you get in terms of IQ.
So there we have it, you asked a question, people gave an answer, everyone's happy ?? Good