Fixed cost versus usage cost
A VPS charges a flat monthly rate whether you serve a hundred visits or a million. A managed platform charges by usage, which is cheaper below a threshold and more expensive above it. The crossover depends almost entirely on bandwidth and function invocations, not on page count. Before deciding anything, pull your actual usage for the last three months and find where your traffic sits relative to that crossover. A single viral week distorts the picture in both directions.