A simple way to value a patent is to set the valuation at the cost of developing the technology.
Cost of Replacement
In the cost of replacement method, you identify the best alternative solution if the technology covered by a patent is not used, and then estimate the added incremental cost of that solution.
In the Market Transaction valuation, one uses the sale of a comparable patent as the value for your patent. The hard part is often finding truly comparable patents, but in many technology areas this is doable. Another drawback is that the comparable patent may have been overpriced or underpriced as part of a package deal. However, it is hard to argue with an actual arms-length sale price as a realistic valuation.
One of the most effective methods for valuing a patent is based on option pricing theory. Using a basic estimate of the market value of a patent and a standard deviation that incorporates risk, you can quickly calculate a patent valuation that considers the many risks of productizing an invention.