In most cases, it is less expensive to purchase products at the physician's office. Physicians are most often obligated not to price a product below a minimum price set by the manufacturer.
One other problem in buying online is that there are many very slick fakes out there. For instance, there was a fake Prevage. This product looked identical to the real Prevage but was a copy from China.
Third, if you have a reaction, the product can be easily returned and your money refunded. This may not be true in buying products online.
Finally, we can judge what products would be best for your skin type. Online companies can not do that.
Thank you for your question.