Cheapest priced copy (Commander Legends: Battle for Baldur's Gate): $0.49 at Card Kingdom, near mint, their price list as of .
Archpriest of Iona 
Creature — Human Cleric · */2 · Rare · Zendikar Rising Promos · #5p
Archpriest of Iona's power is equal to the number of creatures in your party. (Your party consists of up to one each of Cleric, Rogue, Warrior, and Wizard.)
At the beginning of combat on your turn, if you have a full party, target creature gets +1/+1 and gains flying until end of turn.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
5 printings · $0.49 to $0.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander Legends: Battle for Baldur's Gate | 686 | Rare | $0.49 | — |
| Zendikar Rising Promos | 5p | Rare | $0.49 | $0.99 |
| Zendikar Rising Promos | 5s | Rare | — | $0.99 |
| Zendikar Rising | 5 | Rare | $0.49 | $0.49 |
| Zendikar Rising | 316 | Rare | $0.49 | $0.79 |
8 rulings from Wizards of the Coast
- 25 September 2020To determine “the number of creatures in your party,” check whether you control a Cleric, whether you control a Rogue, whether you control a Warrior, and whether you control a Wizard. The number is the total number of those checks to which you answered yes. Each creature you control can be counted for only one of those checks.
- 25 September 2020The ability that defines Archpriest of Iona's power applies in all zones, not just the battlefield.
- 25 September 2020The last ability won't trigger at all if you don't have a full party as your combat phase begins. It won't grant +1/+1 or flying if you don't have a full party as it resolves. The number of creatures in your party may change between these times, however.
- 25 September 2020Some cards refer to you having a “full party.” This is true if the number of creatures in your party is four.
- 25 September 2020If a creature has more than one party creature type, and there are multiple ways to count that creature that could result in a different number of creatures in your party, the highest such number is used. For example, if you control a Cleric and a Cleric Wizard, the number of creatures in your party is two. You can't choose to have it be just one by counting the Cleric Wizard first as a Cleric.
- 25 September 2020Once the target creature gets +1/+1 and gains flying, it keeps those bonuses even if you no longer have a full party later in the turn.
- 25 September 2020An ability referring to the number of creatures in your party gets a number from zero to four. Such abilities never ask which creatures are in your party, and you never have to designate specific creatures as being in your party. You can't choose to exclude creatures from this count to lower the number.
- 25 September 2020Archpriest of Iona's power is constantly updated as the number of creatures in your party changes. If Archpriest of Iona is on the battlefield, it will consider itself as a Cleric.