What caliber? Some calibers (.38 special, .45 ACP) are all/most all subsonic, others give you a choice of either (9mm, .22LR, etc.)
.22LR subsonic ammo is preferred for some competitions, and is more expensive than the cheap stuff, sometimes 2-3x or more.
By the way, selling your own ammo is a regulatory minefield, be prepared for substantial legal costs to do so.