$.$$ apiece at a dealership, about $1.50 apiece on the Help! rack, $8.75 a box of 25 at Fastenal.
Pull the center pin almost all the way out to collapse the rivet. Insert it, firmly push in the center pin to lock. The AuVeCo item may take a bit of judicious tapping with a plastic mallet to seat the pin.
from the handy-dandy gearhead possibles box ......................
There are cars where you have to remove them to change the battery or headlight, and they very often fall apart, or a person (not me) (okay, me) accidentally launches them into space trying to pop them out of place. For some people, it's probably just not worth the trouble to track down a trim retainer that isn't vital to the operation of the vehicle. Of course, if you want it to look right, it's a must-have!
Rat, Radiator sight shield, headlight work - the question for the car in the OPs post. #1.
This same question comes up in these FWD forums twice a year.
Here's the same setup on a late 2002 Seville TS..................... You can see 3 of the 6 retainers. There are over 20 throughout the whole front end assembly, so it makes sense to have a few spares on hand. Post #2. Also note the Christmas tree retainer buttons for the underhood insulation.