Cheapest priced copy (Double Masters 2022): $0.35 at Card Kingdom, near mint, their price list as of .
Deranged Assistant 
Creature — Human Wizard · 1/1 · Common · Commander Legends · #65
{T}, Mill a card: Add {C}. (Activate only as an instant. To mill a card, put the top card of your library into your graveyard.)
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
6 printings · $0.35 to $1.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Double Masters 2022 | 45 | Common | $0.35 | $0.49 |
| Commander Masters | 87 | Common | $0.35 | $0.49 |
| Commander Legends | 65 | Common | $0.35 | $0.49 |
| Innistrad Remastered | 61 | Common | $0.35 | $0.49 |
| Innistrad | 52 | Common | $0.39 | $1.99 |
| Ultimate Masters | 49 | Common | $0.35 | $0.49 |
One ruling from Wizards of the Coast
- 24 January 2025Once Deranged Assistant’s ability has been activated, it can’t be reversed for any reason. If you activate it while casting a spell and discover you can’t produce enough mana to pay that spell’s costs, the spell is reversed. The spell returns to whatever zone you were casting it from. You may reverse other mana abilities you activated while casting the spell, but Deranged Assistant’s ability can’t be reversed. You’ll still have any mana the ability produced, and the milled card will still be in your graveyard.