i am working on my side-product [1] where i was exploring a Rockchip which required external memory (just 1G) which went from $3 to $32 and completely destroyed economics for me. I settled with one with embedded memory and optimizing my code instead :)
I suspect game development will be similar - game companies will optimize their games given customer cards are not going to be released for a while or will be too expensive.
For reference, Octopart is useful to track prices from many distributors, linked below [0] is a commonly used memory (1G) for Rockchip, Amlogic, Allwinner on many Radxa and Orange Pis.
[0] https://octopart.com/part/nanya/NT6AN256T32AV-J2