It's crazy to prefer a natural diamond for anything other than a collectors' item. It's not about being 'cheap' - whatever your budget is, if you're picking an engagement ring say, why not get a technically superior (or larger) stone for the same price tag?
..and add here technically superior plastic flowers with a selection of natural scent sprays :)
Lab-grown diamonds are the same thing as natural, the same material, and can be produced to a higher specification for the same cost as finding (due to scarcity, labour, etc.) an objectively worse stone. (Or equivalently a given spec can be manufactured cheaper than it can be found.)
The correct flower analogy would be growing nicely coloured varieties in a nursery vs. hunting for those random mutations in the wild.
(Nobody does the latter!)