The Cape Verde Escudo (CVE) is the official currency of Cape Verde. The $ symbol is typically used to separate decimals; for example, 20$00 indicates 20 Escudos.
The Cape Verde Escudo is pegged to the Euro at 110$265 Escudos = 1 Euro. Most businesses also accept euros. Banks are found in all the main towns and most have ATMs that accept bankcards and Visa. Credit cards are not widely accepted; Visa is the most widespread.
For more information, see the Lonely Planet Cape Verde Guide or Cape Verdean escudo – Wikipedia.