The definition of compliant is obeying. An example of compliant used as an adjective is a compliant student which means a student who follows all of the rules. complying or tending to comply; yielding; submissive.
We're having the ring bearer wear a tux that is age appropriate. It costs about $70, everything included. Your tux shop should have these or be able to order them. Edited to add: A friend several years ago had a ring bearer in her wedding and dressed him in a shirt and tie instead of a tux.
Consignment shops generally have a wider selection of tuxedos, but prices for basic black will start at about $75 for both pieces, going higher as the style and label improve. At consignment shops, you won't find the deals you expect; sellers usually know what they have and want a return on their purchase.