The cost of a custom chocolate mold greatly depends on the design and mold material. For example, the least expensive type of custom chocolate mold is going to be a simple logo put on a bar of chocolate. The price will start at around $150, though it varies greatly. Most will charge around $300 for this type of mold. The type of mold you will receive for this price is a thin plastic vacuum formed hobby mold that is good for short term use.
Many people want a professional style chocolate mold, hard polycarbonate. No doubt polycarbonate chocolate molds produce the best results and last the longest. However, these molds are made by injection molding and the price is in the thousands. Unless you are having these made for long term, high volume production, you simply cannot justify the cost.
The middle of the road is a silicone chocolate mold, or there are other food grade epoxies that can be cast. These molds will start around $400 and are a good option for getting a higher quality mold, yet not going full blown into an injection mold.
Generally the time to make a mold takes 3 weeks or more. The design process takes the longest in order to make sure the chocolate de-molds properly and that the artwork is satisfying to the customer.