People underestimate the amount of work and technology required to have a fully functional robust marketplace where vendors can list their products, consumers can buy and the marketplace charges a commission.
If you want a lightweight portal to test out the market, you can buy a WordPress theme or a PHP script and we can set it up and tailor it for you. It will serve you initially and if you become popular, we can build you an industrial strength marketplace, custom designed with a backend of PHP or Java. Let's look at your options at various budgetary ranges:
$1000 to $3000: Buy a WordPress theme or a PHP script from Agriya or iScripts and we can set it up for you with light modifications to suit your needs. Time frame 3 to 4 weeks.
$4000 to $10,000: Use an ecommerce platform like Open Cart, CS-Cart or Magento, buy the extensions available for these platforms and we setup and integrate them for you. Time frame 6 to 12 weeks
$25,000 and up. We will build you an industrial strength marketplace from scratch, custom designed with a backend of PHP or Java. It will be able to take heavy loads and grow with you for a long time. Time frame ~ six month
Please note: Building a marketplace is one part of the equation. You must have a separate budget for promoting and managing day to day operations, managing finances, managing disputes, customer service etc.