If you are talking about Finpecia and Propecia(not prepecia) the only difference is that finpecia is a generic version of finasteride, the active ingredient of propecia. Basicaly they are exactly the same thing. There is also Fincar and Proscar witch is the same but instead of 1mg of finasteride it contains 5mg. Fincar may be the cheapest of your option unless you can get your inscurance to cover you proscar(you have to cut it into 1/5ths). If the last the cost is going to be minimum.