If you mean a Crypto exchange platform like LocalBitcoins, the cost of development relies on two important aspects, they are ROI features and elite functionalities.
Considering the development process, you denoted a crypto exchange like Localbitcoins. So it is better to choose a Clone script instead of developing from scratch. Because the development from scratch requires unique coding with deep analysis & high effort that may end in technical glitches and difficulties in deploying the software.
That’s why the replication also called Clone script is mostly preferable for startups. And the cost of the clone script is between $9K - 15K. This cost varies is based on the second aspect called Return On Investments which is called features. This needs for the business to get high ROI. Since this LocalBitcoins clone script replicates all features of its original platform.
To know more about the characteristics that are related to the cost of clone script development, read with the help of this thread to create a Crypto exchange like Localbitcoins. or you can create one on other popularized platforms like Binance, coinbase, Paxful, and more.,