I've been collecting pokemon cards since the Black and White expansion when I was a kid, but never really paid attention to price. I didn't really care that my Reshiram RC22/25 would be worth almost $150 in the future, just that it looked cool. Now that I am older and am actually looking at the prices of these things, I've become more interested in the monetary value assigned to these things. But you guys and how you value things... confuse me. I got 10 packs from Ascended Heroes from a box. I ended up getting 2 Special Illustration Rares, so I imagined I just made my money back. And so, I search for the price of Mega Dragonite ex and find it selling for $850?? 

Now that I'm done rambling, I need to know; is this normal for this kinda thing to happen, or is it just overvalued right now? It's almost as valuable as both Ascended Heroes gold cards combined, according to my price tracker. Why is this the 3rd most valuable card in the set? 

As a side question, do yall have a recommendation for a price tracking app? I'm currently using TCG MasterDex. I've considered Dex but I have enough French, German, and Korean cards to want to track those prices if they're different than English. I do like the degree of organization they offer though. 

I'm kinda new, why is this so valuable??