FWIW, DOT 3, 4, and 5.1 are compatible. The higher the number the higher the temperature range. Sram fluid is 5.1 though they say you can use DOT 4. (DOT 5 synthetic is not compatible.)
In a pinch, I’ve used DOT 3 on my Sram Force brakes and it worked fine. It was what I could buy on the spot at my local store.
It definitely doesn’t seem worth it to buy 4 ounces of Sram fluid for $10-20.