I have a small but decent collection of strategy guides, despite the fact that I don't like to pay too much for them and hardly ever acquire "penny guides." Even the two in my collection that stand out the most - the official Earthbound guide, and a Nintendo Power guide for SMB 3 - were Goodwill finds that cost me 49 cents each.
My record shouldn't be too hard to top - $2.99. Here's the guides I've paid that price for:
The Legend of Zelda: Ocarina of Time - Official Nintendo Player's Guide
Sega Dreamcast Collection - Prima's Official Strategy Guide
And I can't remember if I paid $1.99 or $2.99 for this one, but if it's the latter, then the Versus Books "Official Perfect Guide" for The Legend of Zelda: Oracle of Ages/Seasons is a part of that list as well.
So, what about you? And if there's something you paid a lot for, tell us why.