Under normal driving, the fluid does not need to be FLUSHED until seven years or 105,000 miles, whichever comes first.
AMSOIL ATF, Castrol Import Multi-Vehicle ATF and Valvoline Maxlife ATF are all multi-vehicle fluids that claim SP-III compatibility but are not OEM approved.
Also, you should also be aware that Hyundai uses a chemical tracer in the SP-III fluid. In the event that the transmission fails, a fluid sample is taken and if the fluid is not SP-III, you'll be facing an uphill battle.
You might want to wait until you are out of warranty (the fluid change isn't due until 105k) before switching to a non-OE fluid. The fluid may turn brown, but that's normal according to Hyundai.
11 Prius - 129k - M1 EP 0w20/OE
07 Accord 2.4 - 111k - M1 5w20/FPS Filter
10 Altima 3.5 - 34k - M1 EP 5w30/FU
92 Previa - 160k - Chevron 5w30/Wix