^^^^ I've not been in Brazil for about 5 years so don't take my pricing info as gospel but I'll do my best.
Generally speaking, Brazil shouldn't be too expensive for you, particularly with the Euro doing so well. Obviously, there's a lot of fantastically wealthy people in Brazil so some restaurants and bars will be as expensive, if not more so, than their European equivalents but I'm guessing you're not a millionaire so proabaly won't end up in those areas.
Brazilian food is ace (provided you're not a vegetarian, that is) It's not noted for its culinary heritage but what the fuck do foodies know?
Seeing as you're going to Sao Paulo, the number one thing to do food wise is smoke a big fat "baseado" and go for a "churrascaria".
http://en.wikipedia.org/wiki/Churrascaria
Essentially, you get to eat as much barbecued meat as you want for a flat rate. Hold out for the "picanha", though, don't let them fob you off with the cheap cuts. Sao Paulo and South Brazil is the home of this kind of thing. Expect to pay maybe 20 - 30 Reais per head for a reasonably nice place in Sao Paulo city, although it can be done cheaper.
Sao Paulo is ludicrously ethnically (and therefore gastronomically) diverse, but the biggest communities are Japanese (concentrated in the suburb of Liberdade) and Italian (all over the place). Look out for "rodizios" of either type of cuisine. These essentially operate on the same principle as "churrascarias" but with dishes of those nationalites rather than barbecue stuff. Expect to pay a little bit more for these than the Churrascaria, especially Japanese food.
There's also loads of Middle Eastern people in Sao Paulo (mostly in Sé, which is right in the centre) so you'll find loads of places doing Lebanese and Syrian food. Habib's is a chain of Middle Eastern fast food places which makes good munchies food.
The main Brazilian dish though (which you have to have at leasy once whilst you're there) is the "feijoada".
http://en.wikipedia.org/wiki/Feijoada
It's traditional to have this on weekends, especailly at carnaval time (which is supposedly how it was invented) Would expect to pay less for this than a rodizio (maybe 10-15 Reais) although will depend on where you go. Otherwise, most of the time people eat a combination of rice, beans and meat with this stuff on top (this usually weirds foreigners out at first so you'll get extra brownie points for knowing what it is first time):
http://en.wikipedia.org/wiki/Farofa
You'll come across all the usual street food sellers too. I'd reccomend "espetinhos" (little skewer type meat things) and "coco gelado" (chilled green coconuts with the tops chopped off so you can drink the milk from them)
There's obviously loads of crazy fruits about which you can have in smoothies ("batidas") Try some with Acai in as you can never get that over here and it's well good for you as well as being a unique taste.
Brazilian beer is all much of a muchness. Main brands are Brahma, Kaizer, (incredibly) Skol (yes, the Skol) and Antartica (probably the best, tbh) but they tend to serve it as cold as is physically possible so you can't really tell the difference and you'll often find that the contents of the bottle they bring will be frozen. Expect to pay about 1 Real for a can ("lata") at the beach or in a bar or around 2 Reais for a 600 ml bottle in a bar (nb: it's traditional to share these round rather than drink the whole thing yourself) Draft beer is called "chopp" (pronounced "shoppee") and will probably cost a bit more and isn't as common. Be warned, Brazilian beer is full of additives so will give you a ludicrous hangover.
Drink plenty of cocktails, especially Caipirinha:
http://en.wikipedia.org/wiki/Caipirinha
which is pretty much the national drink and Capeta, which is chocolate with cachaca and powdered guaraná and will send you mental. Cocktails will obviously be a bit more than beers, probs 2 - 3 Reais, more in posher places.
If you can get hold of wine (not common in Brazil), have some of the locally produced red wine (ask for "suave" instead of "seco") It's really sweet and nothing like European wine, goes down a treat. Italian places will usually have this.
Last but not least though, make sure you drink some Guaraná: a soft drink made from the guaraná berry, which is a natural source of caffeine. This stuff is quite possibly the nectar of the gods and gives you a brilliant slow release of energy throughout the day too. The best brands are Kuat (pronounced "Kwachee") and "Guaraná Jesus" (this stuff is bubblegum pink, but is more popular in the North East so you might not be able to get it where you are)