Open-Source vs SaaS: Best Choice for a Scalable Marketplace?

I’m planning to launch a niche marketplace and trying to decide between open-source and SaaS solutions. Platforms like Bagisto and Magento offer deep customization and full ownership, but Shopify and BigCommerce seem easier to launch quickly with less technical work. My concern is future scalability and vendor management complexity. If you’ve built or scaled multi vendor marketplace, did you regret going with a simpler SaaS solution, or was the convenience worth it?

Saas is often cheap at start to get people there but having large site makes you cry to migrate it to solution that is not based on scaling.
Honestly I do not believe there is anything cheaper then osclass + hosting that can go for 50$ per year.