A cool almost-spring night at the end of cold season is probably the wrong time to tell you this, but Costco has a megasized bottle of Infant Tylenol Drops for like six bucks.
Megasize for Infant Tylenol is, of course, 1 oz., but hey. It helps get the kid through the night when she's teething. Didn't see if they had the Cold & Cough variety, too, but they do have the regular pain relief one. It works out to less than half the street price, plus it doesn't run out as fast.
Note: we find the Tylenol eyedropper to be a bigger pain in the butt [because of the riptide when you release the squeegee part] than the syringe that comes with Robitussin, so we swapped it out.
As always, consult your doctor, and don't sue me.