It's quite a large question. I suggest reviewing the environmental valuation research topic if you are looking for a cost. Environmental economists around the world have developed many frameworks. I don't know exactly what your case is but normally un-professional researchers can use the "benefit transfers" as a method to evaluate their concern item. Kindly review this document for your reference: Technical Report The TEEB Valuation Database: overview of structure, data and results
In addition, you should have answers to the below questions once you start:
The first question is: What is your definition of urban aesthetics? Is it about the style of architecture? Or is it about the ratio of green spaces? etc.
Second: What exactly the aesthetic values are about? Is it help to improve tourism interest? Is it help to reduce mental sickness such as depression in the community if they are surrounded by nice urban spaces?
Third: Who are the benefited people? Are they the local community? Are they people who travel from elsewhere?