For your 2 spare days in that city, I think you can visit the Bund and Yuyuan Garden, adn take a Huangpu River Cruise along the Bund on the first day. The left day, pay a visit to Zhouzhuang. For budge hotels, I think you can try East Asia Hotel, Metropolis Hotel or Haigang Hotel. Although their conditions are relatively poorer than the 4-star and 5-star hotels, they are located near to the bund and Nanjing Road.