The value of each of your free spins depends on the type of bonus it is. If it is an in-game free spin bonus, then the value of those spins is determined by your previous real money wager. However, free spins offered as a casino promotion will typically be played at the lowest possible stake which involves all the slots paylines. This is often anything from 0.10 up to 1.00 a spin, seldom more than that.