So, I (and by I, I mean my mother) paid for 2 ssat exams, which totaled to $280 ($140 each). I’m not complaining here as this is an investment for my future, but I’m curious as to why are they’re so expensive.
Can somebody give me an explanation?
Wow, I do remember them costing more than I expected. Maybe it’s the demographic. Also, fewer people take the SSAT so they have to spread the cost of developing the test across fewer people. Just stats.
I don’t know the answer to your question (other than spouting off various economics theories), but when I was applying, as I was living abroad, my test fee was twice the US fee, and skidad had to drive me to a different country to take it. $140 is a bargain in comparison. 
wait until you need the GRE!
Or MCAT.
FWIW, when I was a HS senior, I added up what was spent on SAT/Subject Tests/AP Exams. $1544.50. Yikes!!!
The MCAT is $315 so I guess it’s time to rethink about my dreams of becoming a psychiatrist.
(lol, I’m joking.)
It’s (unfortunately) just economics. Monopolistic pricing. If you had 20 different tests to choose from, all equally accepted, accessible, difficult, etc., you can bet prices would be much lower. At least the SSAT, GRE, and MCAT are the only tests you have to take to get into the respective schools. The amount of testing (pointed out by skieurope) required to get into college (particularly, competitive colleges) is truly out of hand. Thankfully, there seems to be a trend to eliminate many, if not most, of those tests.