Hm. To make it more interesting, I like the idea of paired sheets. What's written on one appears on the other. Typically two sheets are created and each person uses one side, flipping back and forth to read responses and compose replies.
Given your scenario, presumably each student would be assigned a specific page for each class, with the teachers copies bound into book form for easier carrying/reference.
Yes, the premise is that there is a pair for each enchantment, the student has a single sheet, the teacher of multiple students keeps the other sheet bound within a book. This is what I said in my first post.
There should also be a delay. This would make the element of surprise in attacks nearly impossible, since a cheap system alerts it. I would add a delay between writing on one and seeing the message on the other. Higher level castings, far more expensive, can make it more interactive.
I do like the idea about a delay. I'd not want a low level Wizard calling a mentor to swoop in and save the day mid-combat or anything, but still be available to give advice, say, if the party was bunkered down in hiding while the enemy prowled around. Perhaps a minute delay.
Sending is a 5th level spell that allows 25 words to be exchanged, possibly extraplanar.
Message allows a conversation to occur for a fair amount of time, and it's 0 level.
You're overthinking this. The zero-level Message spell already does what you want: to send/receive an AUDIO message via a whisper, so why not simply refluff it to a written message??
Writing on either page activates the enchantment, causing the message to appear on the other end. For simplicity, we'll presume the spell automatically handles erasing errors and auto-clears the page each time a new message is sent. Being a zero-level spell, any 1st level apprentice can lay the enchantment once someone has prepared the surface via Craft Wondrous Object, so our cost to produce would be:
spell(message) zero-level so cost at .5
cast by 1st level wizard 1.0
as a use-activated effect 2,000
and since Message is a 10min/level base spell 1.4
for a total base cost of 1,400gp per student/set.
and doubling that gives us a manufacture's suggest retail price of 2,800gp.
I'm not sure I would assume an autocorrect for erasing errors or anything like that, I'd expect however neat or sloppy the written message is, is how it would be communicated. It would still require a mundane pen and ink to write upon the page.
Erasing the message would be a separate effect than writing it, which is why I foresee 2 spells needing to be put into the Wondrous item to make it work, increasing the price. I do see how
Message would make a reasonable base spell for this item.
For pricing, you can cut 30% by making it only usable by a particular class, and so it this item can be used only by Wizards, we can drop 30% of whatever costs.
I also don't know if making a Wondrous Item that consists of multiple parts qualifies for a higher price. I can't seem to find information on this. I look at the Aspect Mirror as a precedent that says each separate mirror has a cost, where as something like a
Ring Gate has the built in assumption that the cost is for the pair.
Or sheets could be one-use items for a warning system or espionage.
I could see this being a one use item, instead of erasable and re-writable, but that would not serve my specific purpose here. A One time use item would not have the
Erase feature.
