how many years since it has been driven?
if it's quite a few years he should expect to have to put some service into it before trying to drive it.
He should check thru the steering and brakes especially as these are major safety items.
change out all fluids - motor oil & filter, brake fluid, tranny fluid & filter (if it's an auto trans), and coolant.
Check the carb as it may have gotten gummed up by sitting with gas in it for a number of years.
Check ALL fluid and vacuum and emission hoses for drying and cracks - replace any that he has any duobts about. I'd just automatically go thru and replace a few of them on principle such as the two fuel hoses from the frame hardlines to the fuel pump and at the back the two rubber hoses from the gas tank to the frame hardline. Also - the two rubber hoses from the frame transmission fluid cooler hardlines to the radiator (if it's an auto trans), plus the rubber brake lines. These fluid hoses deterioate from the inside so they may no longer be good but you can't always tell from looking at them - they swell up on the inside and won't let fluid thru them.
If the car has AC it most likely will need to be recharged.
If the car is in good condition and has been stored well inside than after all the above has been done there would be no reason that the car shouldn't be just fine.
Price can vary greatly depending on overall condition, options, if it comes with documention. etc but for a low milage good condition '78 Pace car figure in the range of $12k - $25k all depending on the variables just mentioned. A perfect condition car with optional L82 motor, lots of other options, and all the documentation will sell for about $25k - anything less than that on the car with options and condition will lower the selling value of course.
just my opinion and others may say differently