Something in the $30 to $80 range that each groomsman will actually carry: a modest folder with a clean look, or a traditional pattern if the wedding leans that way. Buy them all the same, keep them under three inches, and include a coin with each if anyone might mind the superstition.
Multiple identical gifts at a sensible price, given to people with different interests. That argues for a versatile, unintimidating knife rather than a specialist one: a three-inch drop point folder is the safest choice.
Avoid anything that looks aggressive. It photographs badly and some recipients will not carry it.
$30 to $80 buys a genuinely good folder in 8Cr13MoV or 14C28N with decent hardware. Buy them all the same rather than picking individually, which avoids any question of who got the better one.
Ordering together also helps reach our free-shipping threshold. See the threshold.
Tape a penny to each box. It handles the superstition, it makes a small talking point, and it costs five cents. See is it bad luck to gift a knife.
If you want engraving, plan the timing. See engraving and wedding party gifts.