plenty of options - there was a newly built area within the Shanghai Science and Technology subway complex (take the subway). Shirts for ~100RMB and suits should be from ~550RMB. Be very picky - demand the finish, style and cut that you're after.

ShiLiuPu Plaza is also great but harder to get to if you don't know the area - from YuYuan Gardens, you head east (towards the river).
Good luck!