timing chain

[84LX89GT]

$20 sounds like a good price. When i had my '84 5.0L the timing chain jumped at 150,000 miles and re-used the sprockets (worked fine) and just bought a new chain only. If the engine you have is a '71+ engine i would get a chain and also a crank sprocket since many ford engines had the crank sprocket retarded 4* for better emissions - the way you can tell if this is the case is when you've got the front cover off and have access to the sprocket see if the crank key-way (the thing that sticks up) is lined up with a dot on the crank sprocket. If it is and it doesn't look too worn i'd re-use it. If it's not aligned i'd get a '71 or earlier 360/390/428 crank sprocket - this would give you an extra 20-30 horsepower for a very small price.
Just make sure that the teeth aren't worn and you should be fine with just replacing the chain.
Good luck,