The launch price was more from the fact that it is the first stacked sensor for its size and it didn't have any competition to bring down the price for a long time, the Oly OM-1 and Fuji X-H2s came out in 2022 and they were the most affordable stacked cameras at that time.
Today the OM-1 can be found for less then 1.200 $ but the X-H2s is still maintaining a higher value on the used market. So yus, buying a Sony A9 Mark I is one hell of a deal for its price, 24 MP 35mm FF at 20 FPS (with Sony lenses only, 15 FPS with 3rd party lenses) C-AF and subject tracking including birds and animals (but not Real Time Eye AF for Birds but it works for Animals/Mammals).
The only downside to the older a9 Mark I is the older EVF that halves the resolution every time it has to focus so it ia not as sharp as most 3.6 Million Dot EVFs but it's still usable.
I would be tempted to get an a9 BUT that 15 FPS limit is very frustrating because I LOVE Tamron lenses and are more affordable the Sony's GM and the 200-600mm ... And no teleconverters allowed except on Sony lenses so you still need deep pockets to get the best out of the system.