Figuratively, what one would have to sell or otherwise place as collateral in order to afford something of great expense.
Comes from the fact that, when buying things of great expense, it actually feels as if you are having to offer said appendages as collateral for said item you are purchasing.
A metaphor for the concept of equivalent exchange meaning 'at great personal cost', in reference to something gained.
The phrase may have originated from the legend of Edward Elric, an alchemist who attempted to revive his deceased mother and later restored his brother's soul at the physical cost of his left leg and right arm, respectively.
When one of your limbs is ripped painfully from your body and a group of 12 men, one by one, stick their dicks into the bleeding muscles of your torn off limb and fill it with cum. Eventually the limb will lose blood and discolour but will still be rock solid from the dried cum.