It's myPhone Pocket, Android 6, 512MB ram, 4GB flash. I found it now cheapest for €42 [1], year ago I found it for €39. The only downside is that default apps cannot be uninstalled, that makes the phone almost unusable. It was never locked to any carrier. It's dual sim but I never had sim in it, I use it only as pocket-wifi-browser (102 grams!) and for app development.
BestBuy has "disposable" androids - probably subsidized by the carrier they're locked to. Just checked - $25 for an ATT phone, used to be $30/$40 with/without sale.
[1] https://www.gigastore.sk/4-az-48-vcetne/myphone-pocket-cerny...