Late last year they were talking about $40 for a KWH which compared very favourably to LifePO4 that was more like $130 at the time and Li-ion that was more like $200. However right now on alibaba you can get a 200Ah battery for about $60 and the LifePO4 300Ah are now down in the $50 range which is an incredible drop in the space of 6 months. So in practice they are less dense and more expensive but I think its new technology introduction pricing and at some point it should be about a third cheaper than LifePO4 for the same capacity, all be it a bit bigger and heavier and quite considerably cheaper than Li-ion for the same capacity.
The small 18650 and other small sized cells have started appearing on aliexpress as well so its possible to get those too butt they are a lot more expensive than a basic Li-ion 18650 at the moment for a lot less capacity. I think its mostly the bigger cells that most people interested in Sodium Ion will be wanting (home battery and grid storage solutions and some of the low/mid range cars) more than small cells since typically the smaller stuff you want to maximise capacity even if it costs a bit more and most will want li-ion and ideally the newer nearly solid state li-ion that doubles capacity per KG.