Hallo,
die Tabellen im Spielleiter-Handbuch sind nur Richtlinien und keine festen Regeln. Einige magische Gegenstände wie z.B. der Unsichtbarkeitsring sind halt offensichtlich bseonders nützliche Gegenstände, so dass der Preis nach Richtlinie erhöht wurde.
Das sollte der SL halt immer machen, wenn ein Gegenstand besonders nützlich erscheint. Er kann in Einzelfällen auch den Preis senken.
Ich empfehle dir den Rules of the Game Artikel hierzu, da findest du z.B. auch eine Erklärung zum Ring of Invisibility:
When the Formulas Fail: Table 7-33 provides the basic tool for determining item prices and costs, but many items don't fit the table. Many spells in the game work fine as spells, but spells come with built-in limits on their power, and chief among those is the simple fact that a spell is used up when cast and a character has only so many spells available each day. Many spells become world beaters when they're placed in items that work continuously or in items that can be reused over and over again. For example, a ring of invisibility is a command-activated item that duplicates a 2nd-level spell, and its caster level is 3rd (the minimum to cast the spell). According to Table 7-33, such an item has a cost of 2 x 3 x 1,800 gp (spell level x caster x 1,800 gp). So, a ring of invisibility costs 10,800 gp, right? Wrong, it costs nearly twice that much (20,000 gp) because an endless supply of invisibility spells are worth something extra.
Gruß Zechi