Cheapest priced copy (Throne of Eldraine): $0.49 at Card Kingdom, near mint, their price list as of .
Wildborn Preserver 
Creature — Elf Archer · 2/2 · Rare · Foundations · #650
Flash (You may cast this spell any time you could cast an instant.)
Reach (This creature can block creatures with flying.)
Whenever another non-Human creature you control enters, you may pay {X}. When you do, put X +1/+1 counters on this creature.
Legal inCommanderBrawlStandardPioneerModernLegacyVintage
Not legal inPauper
6 printings · $0.49 to $2.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Throne of Eldraine | 182 | Rare | $0.49 | $0.79 |
| Throne of Eldraine | 375 | Rare | $0.79Out of stock | $2.49 |
| Foundations | 650 | Rare | $0.49 | — |
| Jumpstart 2022 | 738 | Rare | $0.49 | — |
| Throne of Eldraine Promos | 182p | Rare | $0.49 | $1.49 |
| Throne of Eldraine Promos | 182s | Rare | — | $0.99 |
One ruling from Wizards of the Coast
- 4 October 2019If you pay {X} while Wildborn Preserver's triggered ability is resolving, the reflexive triggered ability triggers and will resolve separately. This is different from effects that say “If you do . . .” in that players may take actions after you've paid mana but before the creature gets +1/+1 counters.