Agree that an overly fancy arm is probably unneeded. But since I use the same contraption to maintain and raise my temps as well as lauter, I do need to make sure that I don't have a single stream else it will channel (and I've proven this on accident) as well as need to keep it submerged to avoid excessive HSA. I currently use a bit of 1/4" copper pipe that I wrapped around a wine bottle with a 90 degree bend pointing straight up, then drilled some holes. I then have a copper arm coming straight out horizontally with a 90 degree elbow. I attach the two with some vinyl tubing that can slide up and down the vertical part of the copper manifold.
If it's hard to visualize, don't worry about it, as I'm in the process of ordering some loc-line to attach to a copper manifold to get it to the right height. I'm thinking this will be the better way to go, and for $10, totally worth it.
The problem with a sparge arm is that they typically sit above the grain bed, and if you're going to run anything but water through it, I wouldn't recommend it for fear of excessive HSA. Anything home made you're going to have to find a way to maintain height as it'll change depending on how much grain is in there. And it's not that easy.
If you're not worried about HSA (as in the beer will be drank within a couple of months) then just taking a bit of flexible copper and attaching it so that the return basically runs it along the side of the kettle will probably be sufficient for a RIMS/HERMS, lautering and sparging (if you keep the liquid about an inch above the grain.) The dispersion of the liquid across the very edge and keeping the inertia of the liquid going horizontally vs vertically into the grain should keep channeling to a minimum.
And I would avoid the normal while PVC stuff, I've heard it can add a plastic flavor to your beer. There may be better PVC (the black stuff? CPVC?) that won't contribute flavors if copper's not an easy option.