How much would it cost to set up a small vendor-based eCommerce website like a mini Alibaba, Elance, or Upwork?

Basically, what is the cost of setting up a website where vendors can create accounts and either do work by the hour or sell parts. Additional add-ons would include a chat function between customers and vendors. Are their companies that have templates for these sites? How much might a custom one run? Note: I am not looking to build something as large scale as any of those, but a micro version of one to begin that will serve a particular market. Also, what might the running costs be? As you can probably tell I'm new to this space and will be looking for mentors. Thanks!