Hi Carolyn,
Smartphones can be at U.S. prices or higher. Just like in the U.S. you can get them cheaper by signing up for a contract. But cell phone contracts are only available to citizens and legal residents. I would recommend bringing a smartphone from the U.S. Be sure that it is “unlocked,” i.e. not tied to a certain carrier in the U.S. There are a lot of options on Amazon.com.
Then you can just put in a SIM card from a provider here in Costa Rica for $5 or so. Again, until you’re a resident you have to be on prepaid, or “prepago” line. You just add minutes at the grocery store or wherever you see a sign for your cell phone company by telling the clerk your number and giving them cash. I find $15 lasts me the whole month as far as voice and text. If you use data, or go online, it’ll be more.
The iPhone 5 is here in Costa Rica but it’s pricey unless you get a contract.
On the other side of things, there are plenty of cheap options when it comes to basic cell phones in Costa Rica. Prices start at $20 (although I wouldn’t recommend buying the cheapest model) and go up from there. You can get a decent phone for about $50.