Try to get him to narrow it down to a body type. It will help in the search. The engines are all pretty much the same from there. Body style often determines price and parts availability.

E-Bodies are overpriced. Not for the weak of budget but repro parts are plentiful.

A-bodies are often reasonably priced but if you want big block power some mods usually have to be taken into account. Not a lot but some things are issues, headers, clutch linkage etc.

B-bodies range from dirt cheap to ridiculous depending on year, body and options.

Later B, M & F bodies are cheaper but some parts can be hard because nobody give them respect.

C-Bodies are really cool and often reasonable priced, but parts are hard sometimes because most people don't keep them and most were junked long ago.

Find out how much can he spend and start looking at what he is looking for. Don't jump on the first one unless it is a smoking deal. There are always more out there.