I'm sorry to say that you aren't going to find a ton of help with regards to Hyundai/Kia, especially regarding transmissions around here. I've been struggling with SPIII advice, let along SP-IV. I just don't think there are enough Hyundai/Kia drivers on here, and transmissions already scare the [censored] out of people.
Here is my $0.02;
If SP-IV is like its older brother, SPIII, then the stuff from Hyundai should be the same as the stuff from KIA. The engine and transmissions are the same, so should the fluids. If you look at after-market fluids, they always group the two together "Hyundai/Kia SP-IV" Hyundai is the more "High-end" line, so maybe the dealer thinks they can get away with charging more? Are these prices coming from the same dealer?
Around where I live, there are a couple of Hyundai and Kia dealers, but they are all owned by the same company. Their prices are excessive, especially for what you get. 1qt of SPIII is 9.95/qt, and a OEM filter is 8.95. You can get OEM parts a lot cheaper off the internet.
If I were in your shoes, I would go with the KIA fluid and not worry. I would also check into what it costs at a Mitsubishi dealer. Their SP-IV should be the same too.
I agree with some of the comments above, the only difference is the part number.
Good Luck.
-p