Don't Rent a Tux!
My oldest son is the ring bearer in my brother's wedding this summer. Tuxedo rentals for children are usually the same price, or very close to the same price as an adult rental. However, almost all formal wear stores offer tuxedos for purchase. Instead of paying $120 to rent a size 4 mini-tux, we purchased or own from Al's Formal Wear for just $60! Half the price!
There are also lots of new children's tuxedos on Ebay starting at just $18. I stuck to the one that my sister-in-law to be pick out to be safe, but Ebay is worth checking. We do still have to buy some dress shoes, but now after the wedding, we own a tux to lend to a friend, or possibly for my younger son to wear in a wedding some day. Maybe a Halloween costume???? :)