Busan is similar to Seoul in the fact that Korean, Chinese and English are prevalent throughout the city. The people in Busan, however, have a different accent when they speak Korean. Many people describe it as sounding like they are singing.
The won is used in Busan as well. In South Korea, we have what's called a "T-Money" card. You load money on it, and you can use it on public transportation, in convenience stores and even some restaurants. You can use it all over Korea.
The prices in Busan were the same as Seoul. Something you notice quickly in South Korea is the prevalance of convenience stores. They are everywhere, and everything you find in them is pretty cheap!
I tried Korean sausage for the first time this week! Looking at it, I honestly was not sure what I was getting into, but it was delicious and very filling. I also tried milk soda (exactly what it sounds like), and actually really enjoyed it!