Hi, the best platform to build an ecommerce site depends as there are so many platforms out there based on budget scale and Usability. For simpler stores, Shopify or Wordpress based woocomerce would suffice. For stores that start small but wish to expand in future magento or solidus is the best option out there. Solidus is a little new so Magento would be more reliable. I am quite experienced and well read in launching e-commerce stores and can help you with selecting not only the e-commerce platform but also the right hosts, logistics, User agreements and drafting policies, Payment gateways and SEO Analytics. A lot of these exceed your posted budget, I normally charge around 30k but for the budget you have posted I can do the website design and content with payment gateway integration.