Cheapest priced copy (Commander 2021): $0.49 at Card Kingdom, near mint, their price list as of .
Boreas Charger 
Creature — Pegasus · 2/1 · Rare · Crimson Vow Commander · #79
Flying
When this creature leaves the battlefield, choose an opponent who controls more lands than you. Search your library for a number of Plains cards equal to the difference, reveal those cards, put one of them onto the battlefield tapped and the rest into your hand, then shuffle.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
3 printings · $0.49 to $0.59 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2018 | 1 | Rare | $0.59 | — |
| Commander 2021 | 84 | Rare | $0.49 | — |
| Crimson Vow Commander | 79 | Rare | $0.59 | — |
2 rulings from Wizards of the Coast
- 13 July 2018You can find fewer Plains cards than the difference, perhaps because you don't have that many Plains cards left in your library.
- 13 July 2018If no opponent controls more lands than you, you'll search your library and shuffle it, but you won't be able to find any Plains cards.