you should just be able to add it onto the end:
(abs([Quantity]>0 && [Quantity] <= 23) * ([Price] * [Quantity])) + (abs([Quantity]>23 && [Quantity] <= 47) * ([Price]Range1 * [Quantity])) + (abs(Quantity>47 && [Quantity] <= 131) * ([Price]Range2 * [Quantity])) + (abs(Quantity>131 && [Quantity] <= 199 ) * ([Price]Range3 * [Quantity])) + (abs(Quantity>200 ) * ([Price]Range4 * [Quantity])) + (abs(DarkColor == 1)?(([Price] + 3) * [Quantity]):([Price] * [Quantity]))