Photography and CGI are tools for different constraints. The cheapest route is not determined by a single image price, but by the number of variants, logistics and how often the assets will need to change.
When photography wins
Use photography when the product exists, can be delivered to the studio and natural material behaviour or small imperfections are important to trust.
When 3D wins
CGI becomes valuable when the product is large, not yet manufactured, available in many colours/configurations or needs repeated packshots, close-ups, animation and staging from one model.
A hybrid can be strongest
Use technical 3D for repeatable product views and variants, then photography for lifestyle authenticity or human interaction. The customer cares about clarity and credibility, not which render engine was used.
Source-of-truth discipline
For technical products, geometry, labels, holes, handles, dimensions and colour should come from confirmed product data. AI-generated scenery must not silently modify the product.
Brief before quote
Count final views and variants, list available CAD/drawings/photos, define channels and output sizes, and say whether the asset must remain reusable for future changes.