Oops, I see you actually did link a guide.
Nice.
How about some Gateway 3000/M210 [disassembly](http://www.digitalscoop.net/Gateway Laptop.html)?
$55 for two connectors, one capacitor 2 square inches of PCB and some wire?
I’m in the wrong business.
Here’s the official hardware guide (pdf) which includes directions to remove the keyboard. I think that’s all the disassembly you need to reach the dc jack. Though it might turn out that the dc jack board is plugged into the other side of the motherboard, which would necessitate a much more thorough disassembly…
UPDATE: I decided to buy the entire sub-board on ebay, used, for $28. I managed to get it back together and working on the first try. 
Overall, a moderate PITA.
Thanks for your help and advice, y’all.
You did better than I did. I found out that Dell actually just replaces the motherboard than trying to repair if try to get them to replace it. My dad had successfully soldered a lot of those in the past, but he messed up on my laptop, and it’s bugged me ever since. I know the laptop isn’t worth much now, but it really hurt my grandfather’s finances to get it for me, and I hate that I broke it.
I don’t know why more people haven’t gone to the separate board, or, better yet, a magnetic plug like Apple. I think that plug going bad is the most common problem I have with any portable electronics. But, at least, with, say, my keyboard, I was at least able to wire a DC adapter directly to the battery compartment. I dare you to try to figure out how to do that with the way too many leads on a laptop one.
Screw paying $55 for a jack. Just solder a little pigtail onto that thing and stick a molex or something onto it. 
Yeah, this seems obvious, and yet… enough people are happy to pitch their old laptop and buy a new one, so the manufacturers have little incentive to make their laptops easily serviceable. Ideally this sort of repair should involve a $5 replacement part and no more than 20 minutes of a competent technician’s time.
There ARE some laptops that are designed with serviceability in mind, since they’re often sold to business in large quantities with service contracts (or the customers want to be able to have a few of their IT guys easily service hundreds of laptops.). IMO, they still compromise serviceability a bit too much to get everything in a slick package. Still, after a string of laptops that have died too soon, of something that should be repairable, I’ve decided to pay a premium for “business” laptops that are easy to service. Most of the big OEMs like Dell, HP, and Lenovo have those sorts of laptops, if you know what to look for.
The Apple magnetic plug is patented, so we should see mass market generic adaptation of that particular technology sometime around 2027. Maybe sooner if Apple needs some cash and licenses it out.