Don't know what you are referring to by "this procedure". If you are referring to the algebraic formula of computing WTP, then you'll need to somehow convert the 3 levels of price into a single price coefficient. This can be done using a linear price term, though it assumes a single slope for a coefficient that could have a kink. Or (discarding some information) you could just pay attention to the two extreme levels and assume a linear function between them.
If you are referring to estimating WTP using the method of market simulation: setting a test product at a given price against a field of competitors, then enhancing the test product and changing its price until the new share of preference matches the old share of preference...then it doesn't matter how many levels of price you have because the software and the mathematical approach can handle interpolation between levels.