K.C.
When my son was in a wedding, we got him a tuxedo at Men's Wearhouse.
If he's not in the wedding, you might not need such a formal outfit. At every other wedding we've been to, we put my son in nice slacks (khaki or navy) and a button down shirt. Sometimes a sweater vest too. You can get those things pretty cheap at Gap and Old Navy. Plus, he could wear them again vs a suit/tux that is a one time only outfit.
K.
http://www.discoverytoyslink.com/karenchao