I just bought one of the Solar S5M's on Ebay from a reputable seller (100% pos.fdbk) for $17.49 US) so ...
LINK:
https://www.ebay.com/itm/165659847094
I previously bought a Diansheng 5×5 from TheCubicle ($13ish) but it was the first basic model (very Meilong-ish) not the Solar series at all and they refunded me, even gave me a shipping label for the return (they're pretty great there really)
So we will see (in 3-10wks, seller is on China ha)
I picked up the Solar S4M a few wks ago and quite enjoy it (much nicer than the S6M and S7M), so I am anticipating a similar quality feel + experience with the S5M...
Fwiw, I like it better and it's more stable than the MGC 4...
(tho I am not particularly good or fast at 4×4)
I think this means they are making all the way UP as you suggested but they might only be following thru on the lower order cubes they already promised (it did take a while before the S4M came thru)