Ever heard of the Captain Hostel? Really cool little place, cheap, and practically right on the Bund. See the ChinaTravel.net hotel page by copy and pasting this URL:

http://www.chinatravel.net/china-hotels/captain-hostel-/introduction-35.html

Well, you can actually stay in a comfortable hotel in Shanghai and pay a much cheaper rate than in the West, you don't necessarily have to share bunks with a bunch of backpackers. The Baron Business Hotel has rooms for about US 60$ a night and is a 3-4 star hotel, you can see the hotel page by copying and pasting the URL below:

http://www.chinatravel.net/china-hotels/shanghai-baron-business-hotel/introduction-12735.html

How much could you afford it? When will you stay in China?
As I see, all the prices of hotels during the EXPO have risen.
But I think if you choose the cheap hotel chain like 7days inn or Green Tree inn. It would not be too expensive, 200 RMB per day. I suggested that you can find a hotel which is just close to the metro station, Shanghai's metro system is rather convenient, you can get to the EXPO pavilion rather easy.
http://www.998.com/eng/index.aspx
http://www.7daysinn.cn/

There's a Green Tree Inn at the corner of Zhaojiabang and Ruijin Nan Lu, not walking distance from the Expo, but just a 5-10 minute cab ride from the Puxi side entrance. CT.net has more on that here:

http://www.chinatravel.net/china-hotels/GreenTree-Inn-Shanghai-Zhaojiabang-Hotel/introduction-5238.html

CT.net's got a google map of hotels you can check out too, right here:

http://maps.google.com/maps/ms?hl=en&ptab=2&ie=UTF8&oe=UTF8&msa=0&msid=111549676436204199752.00048144d52f8a50569db

if you are searching for a cheaper accommodation in Shanghai I know a good option, the homestayglobal can provide perfect accommodation for you as a homestay，where you can get good opportunity to improve your Chinese language and know about the culture of China. You will be provided with well furnished room with internet facilities. Visit homestayglobal website for more information

Fairmont Peace Hotel has finally opened, along with Waldorf Astoria. More are coming.

Hotel Pravo (http://www.hotel-pravo.com), Shanghai – located on North of The Bund, will actually be the first of boutique suite collection set to open in Winter of 2010. The hotel will house two gorgeous restaurants, one of which is notably serving Chinese Imperial cuisines fit for an emperor. The hotel’s lobby area will be filled with contemporary art piece by Xia Xiao Wan.

http://hotelpravo.wordpress.com

Just go to www.guideshanghai.com and book a place through them. They have lots of hotels on their website, some big western ones like the Hilton etc and some big Chinese ones but either way they offer great deals. Mostly 4* and 5* so not for backpackers but quality is quality.