G rosea is the most common species in the hobby, bar none. Smithis are just better known as they photograph well.
You wont really notice the difference untill they get older then they are a lot easier to tell apart then. I have 1 smithi and 2 annitha slings that are starting to show markings but no colour yet. The carapace is the best way to tell them apart as the smithi contains a lot more black as opposed to the annitha also the annithi as orange that is a lot more vivid leaning more towards the red of the auratum. Finally as adults the annitha in theory should be larger and leggier than the smithi but until then I'd make sure you label them lol
Ditto to Bob’s and Rick’s comments above. Red-legged Brachypelma are much more difficult to breed than their non-red-legged relatives (vagans, albopilosum, etc.). The methods to breeding smithi are known but not so easy to reproduce, and those to breeding annitha are essentially unknown except to a few. Indeed, overseas, annitha and its cousin baumgarteni are considered essentially impossible to breed. That helps explain some of the price differential, but there is more:
That's a good idea. Maybe instead of breeding their rose hairs all the time, more people can focus on breeding less commonly available or difficult to breed species.