Dollar alternative (4)
'dollar alternative' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for avis that I've seen before include "Unusual bird or extraordinary person - rara ?." , "Rara --, rare bird (or car rental firm)" .)
(Other definitions for euro that I've seen before include "Continental purchaser" , "Modern cross-border currency" , "Continental currency" , "New currency" , "International monetary unit" .)