
Anzyr |

Most of the Adventure Paths go to level 20 (except Council of Thieves I think). The Rise of the Runelords boxed set PDF version can be had for 41 dollars.
Even better the entire set of Iron Gods Adventure Path PDFs can be picked up for $15 on the Humble Book Bundle running right now. It will only take you to level 17 though.

Steve Geddes |

Most of the Adventure Paths go to level 20 (except Council of Thieves I think). The Rise of the Runelords boxed set PDF version can be had for 41 dollars.
None of the post dungeon APs go to level 20, except for wrath of the righteous (which also uses mythic rules).
Shackled City, Age of Worms and Savage Tide all go that high, but it's not trivial to track them down as they weren't all converted to PDF and only shackled city was compiled into a hardcover.
As an alternative, if you're stuck with a sub- 20th level AP, you could try working out what level the campaign was going to finish at and granting PCs their class's capstone ability at that level. I've had some success doing something like that.

LegitName |
I picked up Iron Gods through the Humble Bundle. Right now we're doing Emerald Spires. Then I will GM Rise of the Runelords (I hear it goes to level 17-18ish). After that I think we'll do Iron Gods or maybe the 20 something Year of the Demon Modules that I picked up as well. I'm trying to design a Super Dungeon/Campaign that will take us pretty far. Hopefully I finish in time.
Wrath of the Righteous sounds fun. I'll definitely look into it. What is Age of Worms, and would I have to buy all 12 of the $5 pdfs to do it?