Those unofficial sources are correct
The Player's Handbook on Writing a New Spell into a Spellbook says that
Once a wizard understands a new spell [from a scroll or another's wizard's spellbook], she can record it into her spellbook.
Time: The process takes 24 hours, regardless of the spell’s level.
Space in the Spellbook: A spell takes up one page of the spellbook per spell level, so a 2nd-level spell takes two pages, a 5th-level spell takes five pages, and so forth. Even a 0-level spell (cantrip) takes one page. A spellbook has one hundred pages.
Materials and Costs: Materials for writing the spell (special quills, inks, and other supplies) cost 100 gp per page.
Note that a wizard does not have to pay these costs in time or gold for the spells she gains for free at each new level. She simply adds these to her spellbook as part of her ongoing research. (179)
These aren't all the rules for doing so, and the entire process is pretty complex. I urge reading the Player's Handbook on Arcane Spells (177-9) to better understand the wizard's adding-spells-to-a-spellbook mechanics. (There's also a summary at the beginning of this answer.)
A wizard can prepare spells from another wizard's spellbook without transcribing the spells into his own spellbook
This is nominally free if the spellbook's already been liberated from another wizard. Doing so requires a Spellcraft skill check (DC 15 + spell level) per spell (Player's Handbook 82-3)