Cheapest priced copy (Commander Masters): $0.69 at Card Kingdom, near mint, their price list as of .
Hangarback Walker 
Artifact Creature — Construct · 0/0 · Rare · Magic Origins · #229
This creature enters with X +1/+1 counters on it.
When this creature dies, create a 1/1 colorless Thopter artifact creature token with flying for each +1/+1 counter on this creature.
{1}, {T}: Put a +1/+1 counter on this creature.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
8 printings · $0.69 to $89.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander Masters | 951 | Rare | $0.69 | — |
| Edge of Eternities Commander | 139 | Rare | $0.69 | — |
| Jumpstart 2022 | 772 | Rare | $0.99 | — |
| Kaladesh Inventions | 13 | Special | — | $89.99 |
| Magic Origins | 229 | Rare | $0.79 | $8.99 |
| Love Your LGS 2020 (Mechagodzilla, Battle Fortress) | 2 | Rare | — | $8.99 |
| The List | ORI-229 | Rare | $0.69 | — |
| Secrets of Strixhaven Commander | 348 | Rare | $0.69 | — |
2 rulings from Wizards of the Coast
- 22 June 2015If enough -1/-1 counters are put on Hangarback Walker at the same time to make its toughness 0 or less, the number of +1/+1 counters on it before it got any -1/-1 counters will be used to determine how many Thopter tokens you get. For example, if there are three +1/+1 counters on Hangarback Walker and it gets four -1/-1 counters, you'll get three Thopter tokens. That's because Hangarback Walker's triggered ability checks the creature's existence just before it leaves the battlefield, and it still has all those counters on it at that point.
- 22 June 2015The value of each X in Hangarback Walker's mana cost must be equal. For example, if X is 2, you'll pay {4} to cast Hangarback Walker and it will enter the battlefield with two +1/+1 counters on it.