The cost to start an online store splits into four buckets: platform and tools, product and inventory, getting found, and the costs nobody warns you about. The first bucket is small and predictable. The second is where almost all the money goes, and it varies...
The short answer: dropshipping is the cheapest to start and the hardest to defend, private label costs the most upfront and is the only one of the three that builds a real brand asset, and print on demand sits between them with almost no inventory risk but...