Is it actually cheaper to leave Webflow for a custom stack?

Often it's the opposite. Once you add up the pieces a custom build needs — a headless CMS, a deploy platform, hosting, and the developer time to run it — the total usually exceeds what Webflow cost. One team that made the switch reported paying $150/month for Sanity and $150/month for Vercel before hosting, more than their old Webflow bill.