Cheapest priced copy (Mirrodin): $3.49 at Card Kingdom, near mint, their price list as of .
Quicksilver Fountain 
Artifact · Rare · Mirrodin · #233
At the beginning of each player's upkeep, that player puts a flood counter on target non-Island land they control of their choice. That land is an Island for as long as it has a flood counter on it.
At the beginning of each end step, if all lands on the battlefield are Islands, remove all flood counters from them.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
1 printing · $3.49 to $12.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Mirrodin | 233 | Rare | $3.49 | $12.99 |
2 rulings from Wizards of the Coast
- 1 December 2004The timestamp of the land-type-changing ability is set when the triggered ability resolves (so each one has a different timestamp).
- 1 December 2004The land stays an Island until the flood counter is removed, even if Quicksilver Fountain leaves the battlefield.