I don't think you have to stay in a hotel close to the expo. These hotels are expensive during the Expo, and on the other hand, many kinds of public transporation have been built accessing to the Expo, special metro lines and city-buses. So, you could get to the Expo site easily then.

So, I suggest that you book a hotel along Nanjing Road, such as the People's Square or the Jing'an Temple. Both of them are not far from the Expo, and also the most prosperous shopping and dining area.