The situation right now with the Doogee U10 tablet: not commonly available.
Once the news gets out about epic breakthroughs on commodity hardware and devices, there's unfortunately a likely spike in the purchase cost, even if such devices can be found at all anymore on the usual online sources of new and used goods.
After seeing the headline I immediately checked eBay and they are available to ship to the United States for $80 total.
I went on Aliexpress and I seem to be able to get it for 73 euro.
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Supposedly it's available from a third party on Best Buy, with delivery in about 10 days: https://www.bestbuy.com/product/doogee-u10-android-13-tablet...