As with Vehicles and crew, there's no mechanical connection between a Mount and its saddle ability
Whichever version of the deck you prefer, youd better hurry up if you want to enjoy it in Standard
You can also break the symmetry of board wipes during the deckbuilding process, like if you run Bane of Progress in a deck without any artifacts/enchantments, or Retribution of the Meek in a deck without any creatures with power 4 or greater
If the price for you is over this, you're usually better off buying singles
It will keep going down to about the $10 mark, and then go back up to around $20, which is the typical slow ascending price cycle of any expensive reprint in Magic: The Gathering
Dialga's status as a cover Legendary from Generation 4, one of the most beloved generations in the franchise, provides a nostalgia floor that keeps demand elevated among the massive Sinnoh fan community