Only place that I've found shirts that fit my frame is Jos. A Bank. A bit pricey, but durable and fairly fashionable. And stuff goes on sale there all the time.
Pants? I never spend more than $30 on a pair of pants. Our profession destroys them - rubbing on a drum or carrier, keys in the pocket brushing up against the wall, kneeling on a football field, etc. Just get what fits.