https://arstechnica.com/gadgets/2018/11/microsofts-special-costco-surface-go-is-now-available-to-all/

Surface Go is Microsoft's cheapest Surface 2-in-1 available: $399 gets you a Surface Go with 4GB RAM and 64GB of eMMC storage. But the next step up in specs was a lot more expensive: it takes an extra $150 to double the RAM to 8GB and replace the 64GB eMMC with a 128GB SSD, a change that should provide a healthy boost in disk performance.

Strangely, there was no model that split the difference; a 4GB machine with 128GB SSD would be a lot more practical for many users. That is, unless you chose to buy your Surface Go at Costco, where a special 4GB/128GB system was sold. Now, however, that spec is available to all through the Microsoft Store, for $499.