I suck at math, but luckily Frank Karsten covered this very problem in an excellent article that I highly recommend reading
Umbreon (Master Ball Holo) While theyre not as elusive as Special Illustration cards, Master Ball Holos are still highly sought after by collectors today, especially this copy of Umbreon from Prismatic Evolutions
An awesome threat for a x deck
Potentially giving a larger stat boost than cards like All That GlittersAll That Glitters and Adaptive OmnitoolAdaptive Omnitool, the Machinist's ArsenalMachinist's Arsenal giving the creature the Artificer type might not have meant much a few years ago, but with a growing influx of Artificers in the game that care about the type, such as Cid, Timeless ArtificerCid, Timeless Artificer, it matters now more than ever
Tarkir: Dragonstorm has powerful cards, and is new enough to be Standard-legal, but old enough to dip down from it's peak price