What factors influence and what components make up the price of creating such a site?
Depending on the business logic, design and additional functionality, the cost of development can vary at times. So I would not try to calculate the amount yourself, and asked for a calculation to professionals who understand the nature of the work.
The cost of developing a marketplace depends greatly on the specific business: you can create a marketplace based on "boxed" solutions or order individual (custom) development. Yes, many people decide to save money and choose the first option, which is not always correct. In general, the topic is very vast. I advise you to read https://www.codica.com/blog/how-much-does-it-cost-to-build-marketplace-website, maybe then it will be clearer where to start.
Starting an online marketplace is one of the best things to do if you want to make a product catalog and sell it. There are millions of potential clients, huge amounts of competition and, on top of that, the right product marketplace builder will help you considerably. With the help of such a tool, creating a marketplace will be quicker and easier than you can even dream about.