I'm going to attempt to construct my own answer to the ChicagoWiz's query: "Copying a spell into a spell book. How long does it take and how much does it cost? Go ahead, look it up in the three core AD&D/1e books." I haven't looked at the comments, so you can compare my answers to other folks and see what we come up with.
Unearthed Arcana, page 79 explicitly notes that putting spells into spellbooks costs 100gp per level of the spell. That falls outside the parameters Chgowiz established, but I thought everyone should know that. Time is not specified. I'd check the official errata for UA published in the Dragon, but then I might be tempted to look in the Sage's Advice column for more info. That way lies madness. And Skip Williams.
There's no explicit answer to the ChicagoWiz's inquiry as far as I can tell, but there are two useful vectors for coming up with your own answer. The first one, which he correctly identifies, is the scroll manufacture rules on page 117 of the DMG. A scroll takes one day per level of the spell. I think that would mark an upper limit for spell transcription times, as making scrolls is clearly meant to be a pain in the ass. For crying out loud, you need a basilisk eye and three cockatrice feathers to make a scroll of protection against petrification. I need the ding dang scroll before I collect that crap, not after!
The other vector is the write spell (PHB 69, DMG 45). Write is designed to make it possible to transcribe spells you don't understand. Like weapon speed factors or training costs, you can tell whether a campaign is hardcore by whether this spell ever comes into play. Anyway, write identifies both time and cost for using this spell to copy other spells. It takes one hour per spell level and you have to pay for the ink. A vial of ink good for 2-4 spells costs 200-500gp, if you can find it. Each apothecary and alchemist in a town has only a 10% chance of having the right kind of ink in stock. In cities the chance is 20% per location.
(If you can't obtain the ink at a store, you can make it yourself. No direct guidelines are given for this, but the scroll manufacture rules indicate that giant octopus or squid ink is a necessary component for scroll ink so that's a good place to start. Incidentally, Hacklopedia volume VI lists giant octopus ink at being worth 400gp. Say what you want about HackMaster's tone, the guys who wrote it have a really strong grasp of lots of little fiddly bits of AD&D.)
Write puts the caster into a trance, which you could argue allows them to transcribe a spell much faster than the normal method. But I think that if Gary intended the spell to double as a quick-copy for understood spells he would have noted so. Therefore, I submit that once a spell is read and understood it only takes one hour per level to put it into your book. The trance is solely for the caster's holy guardian angel/unconscious mind to do the heavy lifting of comprehending the spell sufficiently to avoid transcription errors.
Similarly, I think the special ink for write represents a hard limit on the cost of normal transcription. Is the same ink needed for both types of copying? That would probably result in wizards spending more time hunting giant squid than any other activity, which cracks me up but doesn't sound plausible. No, I think significantly less awesome ink will do. Unfortunately, I can't find ink is on any official equipment list prior to Oriental Adventures (where it costs 3 tael, i.e. 30sp, for an unknown quantity). We're left with a best guess at this point. So here's what I would rule if attempting to run pre-UA AD&D as written:
Cost: 20-50gp for ink, which lasts for 2-4 spells
Time: one hour per spell level
That's a lot faster and cheaper than I expected when I started cracking open books.
2 hours ago