Vodafone as a shop right in the Schengen terminal just after you leave baggage control where obviously the people speak English so they'd be able to sell you the SIM and get it activated.

Otherwise in the CR you can buy a SIM or top up credit at any "Tabac", their word for mini-convience store that sells magazines, cigarettes, drinks. Plus of course all around the city center are shops for the major carriers, Vodafone, T-Mobile and a couple of others.

Unlike some countries, the reason you can get them in any shop is you don't need to have your personal data entered. One of the easiest places to get a SIM.