FOOD: If you're shopping at a grocery store in Costa Rica, be careful because it could quickly turn into a very expensive trip. However, if you're a savvy shopper you'll be just fine. The reality is if you buy the local products and brands, the prices are comparable or even a little cheaper than products in the US. However, imported goods are what's going to kill you. The Americans that come down here and try to eat their usual diet are the ones who pay for it. For example, peanut butter is $5 for a small jar, chocolate chips are $7/bag and American cereal brands go for $5-7/box. Produce is the same way. If you buy locally grown produce, it's extremely cheap. Things like bananas, limes, plantains, coconuts and papayas are extremely affordable. On the other hand, things like apples. berries, peaches and oranges are going to cost you. You'll find the cheapest produce at the weekend "ferías" (farmers markets) where you can get "un mano" (a large bunch) of bananas for about 75 cents or 15 limes for a dollar amongst other incredible deals. For anyone looking to save money in Costa Rica, take my advice: eat like the locals and shop like the locals. This means rice and beans everyday and shopping for your produce at the weekend ferías.
ELECTRONICS: No contest here. Costa Rica is definitely more expensive. And if you think about ordering from the US and having it delivered here to save money, guess again. You'll get slammed with import taxes and postal fees. This is why many Costa Ricans take annual trips to Florida to do their christmas shopping and save hundreds if not thousands of dollars on electronics.
CLOTHES: Once again, Costa Rica is more expensive than the US. Think of the price your favorite item from Gap, Forever 21, Express or another American brand and add another 25-50%. That's the Costa Rican price. One of my students recently paid $80 for a pair of TOMs shoes and Converse cost upwards of $100.
RENT: Finally, a category where Costa Rica is cheaper. I live in what's considered a nice neighborhood of a metropolitan area and I pay the equivalent of $240/month utilities included. Most of my friends in the US pay double, triple or even quadruple that for the same kind of living situation.
CARS: Costa Rica is by far more expensive in this category. Take the price of any american car, and then add another 50%. That's the Costa Rican price. However, car rental here is about half the price as in the US so I'd definitely recommend taking advantage of that if you're on vacation here.
HOSTELS/HOTELS: Tourism is one of Costa Ricas major money makers, and they know it. However, the US has pretty steep prices when it comes to hotel stays too. Costa Rican prices are comparable to the US ones. Since we don't have many hostels in the US, I don't have much to compare to there. However, I have lots of experience with european hostel prices. The reality is that most hostels in Costa Rica are comparable to european prices, however there are a few locations where you can find rooms as cheap as $7/night.
EATING OUT: Going out to eat in Costa Rica is about the same as the US, about $10-20/meal (depending on how nice the place is). Furthermore, if you go to a US chain like Applebees, Chilis or Outback Steakhouse (I don't know why you would... but just in case) be prepared to pay more than you would in the US. However, there are a few exceptions to the rule that dining is more expensive here. Eating a local "sodas" which are diners that serve typical Costa Rican food will save you a LOT of money. You can get a big plate of rice, beans, salad and a protein with a drink for as little as $5... and it's really darn good too.
ALCOHOL: I don't know why, but it's cheaper to buy a beer at a bar, but it's more expensive to buy a beer at a store in CR than the US. Haven't figured that one out yet. Similarly to food, you'll pay a lot for an imported beer or alcohol. Wine here is expensive, and it's not very good. However if you're looking for a cheap drink, guaro will be your saving grace. It's a local liquor made from sugar cane that sells for about $8/liter. It's like a cross between tequila and vodka and many times is served in shot form with a spicy tomato juice. I'm not a huge fan, but like I said, huge money saver.
PHONE PLANS: Costa Rica is the winner in this category. I pay for a pay-as-you-go plan here in Costa Rica. I recently just put on $8 and it lasted me a month... data and all. The same amount of data would cost me over $50 at least in the US... no thank you.
GAS: US wins again. US gas is currently about half the price of Costa Rican gas.
MEDICINE: Found this out the hard way when I payed $20 for a bottle of milk of magnesia that probably would have cost $7 in the US this weekend. Seeesh. I definitely will be avoiding the hospitals and pharmacies at all costs while I'm here.
In summary, where are you saving money in Costa Rica? Local produce/ food products, phone plans, rent and... that's about it. It's a huge misconception that Costa Rica is a cheap country to visit or live in. If you're looking for a more affordable vacation or place to live, you can travel just a few hours away to bordering Nicaragua or Panama. However, I am living in one of the greenest, happiest, most diverse, most beautiful countries in the world... so that's the trade off. It truly is the price of living in paradise.