There is no definition of right price. This depends on your estimation, how much are you willing and can invest and how much risk you are ready to accept.
Basic rule for trading is to buy low and sell high but in practice this is not always easy to do because it's hard to predict the movements of price. That is why good traders need to have a lot of knowledge and experience to be able to judge properly conditions on the market and when is the good moment for investing. That isn't easy and that is why we don't have much good traders who are able to make decent profit on a regular basis.