My Perverse Equivalent Exchange System in Doomsday

One cannot gain anything without first giving something in return. To obtain, something of equal value must be paid. The life saving system that Long Yu received supposedly follows this rule. Unfortunately, the price required some times can turn out to be somewhat strange. 'System, I want to exchange for something that can regrow an arm.' Searching.... Recommended option: Limb regeneration capsule Price required- 20kg of mutant lizard fertile semen '.....' P.S. This novel has nothing to do with F.M.A (Full Metal Alchemist) just in case you were wondering.