Goa isn’t a city, it’s a state of mind. It’s also a state in India, which contains several dozen small towns, many of which are along the beach and attract big numbers of tourists from November through March. Compared to most of the rest of India prices in Goa are relatively expensive, but compared to nearly anywhere else this place is a bargain.
During the peak travel weeks from Christmas to New Years the prices do go up and hotels are packed so if your schedule is flexible that is the time to avoid, or be prepared to pay more. Still, hotels in Goa are cheap and fairly good standard for a beach resort area. Hotels at the bottom end of the range will be quite minimalistic though, so be prepared. Also, choose the city you stay in carefully. Some are more known for parties and others are more known for family holidays.
The main attractions are sitting around on the beach all day, and going to bars and clubs or even beach raves at night. All of it is either free or quite cheap, so once you get here you can get by on very little. Even the food and drinks at the many beach restaurants are in line with places in town, so having drinks and a meal on the beach is definitely a bargain compared to Europe.