Cheapest priced copy (Fallout): $2.99 at Card Kingdom, near mint, their price list as of .
Well Rested 
Enchantment — Aura · Uncommon · Fallout · #88
Enchant creature
Enchanted creature has "Whenever this creature becomes untapped, put two +1/+1 counters on it, then you gain 2 life and draw a card. This ability triggers only once each turn."
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
2 printings · $2.99 to $34.99 at Card Kingdom
One ruling from Wizards of the Coast
- 8 March 2024If the ability granted by Well Rested triggers in an untap step, it goes onto the stack at the beginning of the next step (usually the upkeep).