Seems to me a "scroll" is defined:
DMGp.199:
SCROLLS
A scroll is a spell (or collection of spells) that has been stored in written form.
If this is the definition of a scroll, then:
PHBp.84:
SCRIBE SCROLL
...Scribing a scroll takes 1 day for each 1,000gp in it's base price.
Seems kinda clear. That said, scribing a spell in a spellbook:
PHB.p155:
Writing a New Spell into a Spellbook
Time: The process requires 1 day plus 1 day per spell level.
...Space in the Spellbook: A spell takes up 2 pages of the spellbook per level.
...Materials and Costs: Materials for writing the spell...cost 100gp per page.
Replacing and Copying Spellbooks
...Duplicating an existing spellbook... The time requirement and cost per page are halved.
What does this mean? Spellbooks are expensive and take
lots of time:
12th lvl caster - 6th level spell:
Scroll: 900gp (6th lvl spell * 12th level caster * 12.5gp) and 1 day
Spellbook: 1200gp (12 pages) and 7 days
Why the comparison? Well, lets look at lower level spells:
5th level caster - 3rd level spell (say, haste)
Scroll: 187.5gp and 5 spells in a day vs
Spellbook: 600gp and takes 4 days
The scroll scriber can make 3 spells on one scroll in one day for
the same cost as scribing haste into your book in four
days.
Now - Is this a major problem? At 3rd level a Wizard
starting gold is 2,700gp (or 80 1st level spells and 40
2nd level spells - scribed in only 2 days no less; Of course,
these would be unmanagebly large scrolls). Additionally,
you would pay the cost in XP.
Conclusion: I would say you need to limit the physical
size of a scroll to a manageable level - say six or fewer
pages/feet.
All of the above said, the SRD has a few discrepancies
to the DMG:
SRD:
http://www.opengamingfoundation.org/srd/srdmagicitemsscrolls.html:
SCROLLS
A spell on a scroll can be used only once. The writing vanishes from the scroll when the spell is activated. Using a scroll is basically like casting a spell.
Physical Description
A scroll has an AC of 9, 1 hit point, a hardness of 0, and a break DC of 8.
So, the physical description does not mention multiple
spells on one scroll. However, check your 3e modules, you
will find bad guys running around with scrolls of multiple
spells.
So, kind of a long post - but I really wanted to look into this
topic. I would go with the physical limitation before the
financial.
Of course, I could be wrong. Your DM is the final judge
after all.
~D