How formal is this wedding? A children's second hand store would have suits and suit jackets as these never wear out since kids grow out of them before having to wear them again. My son is a giant - and always has been. He was a ring bearer in his cousin's wedding and we had to rent a tux. It was $100 but came with shoes. My niece offered that he could wear a suit - but we knew he's have no need to wear it again so we just rented it. In the month between the fitting & the wedding he grew and the tux barely fit him!
For my other niece's wedding he wore dress slacks, a nice collared shirt and tie - no jacket. It was pretty formal - at a catering place. But it was in the the Summer and I knew most men would have their jackets off within 10 minutes. So I decied not to spend $100 for 10 minutes.
He's now 13 yrs old and 6'2" and my mom is in hospice now so we are planning her memorial service and again, I don't think I'm going to get a jacket for him since I know he'll never wear it again. Even shoes - ! Maybe I'll call the mens shop that we rented the tux from...