Siamese Tigers or ST are by far the most expensive datnoids. If you're new to datnoids it might seem a bit strange that two fish that look so similar have such dramatic price differences but let me tell you from one of us dummies who would pay an extra, "0" to the price for a seemingly identical to most people fish there IS a reason for the disparity.
For simplicity sake I'll just say a generally true statement, all datnoids are wild caught. There seems to be a slowly growing exception with ST now being bred in captivity though this could possibly still be disputed as I'm sure none of us users here have seen this breeding program with our own eyes (correct me if I'm wrong anyone, I'd love to learn more about it). This is one of the main reasons datnoids have a slightly to noticeably higher price than similar large fish in the hobby, there's a limited supply in their natural habitats which between food fishing and damming continues to struggle in most areas. ST for some time were/are for all intents and purposes are considered highly endangered or extinct in most if not all of their natural habitats.
ST have come to this fate largely due to their desirability for their more outgoing and brave personalities, more active nature than other datnoids on average, stout, taller bodies and most of all their stability.
ST and IT at a glance or to the untrained eye look the same. This is where the confusion about the price difference comes from. Upon closer observation IT generally have a more brownish-yellow coloring and don't on average show out their full beauty, golden color, solid black bars as their ST counterparts whereas ST much more often show their more golden/white-yellow with solid black bar coloring. In addition the number of stripes as a general rule comes into play. The tail stripes are the biggest giveaway with ST tail stripes connecting to one another and the body bars generally being one large, sloped back bar opposed to the common "4 bar pattern" IT poses.
Again, not to steer you away but I highly recommend checking out the Datnoid ID sticky thread for more information on deciphering the differences between the two.
TLDR;
ST = prettier goldfish yellow, more stable color, more personable, taller bodied, most of all much more rare
IT = more brownish yellow, generally less stable, less tall bodied, more abundant
BUT if we're not careful IT will go/is starting to go the same way of the ST if we don't make sure we help in preserving the wild populations until some reliable breeding program can sustain populations. My advise, if you get a datnoid, stick with it. Grow it big and love it for everything that makes is unique in our hobby. Don't just keep it a few months then pass it on. These fish aren't guaranteed a tomorrow and when they're gone they're gone. I for one would like to keep datnoids until the day I die and we all have a part in making sure that is possible down the road.