Upload & Sell: Off
...Without assuming too much, is it safe to say that ANY Canon flash with an "EX" at the end of the number will work properly for both cameras?
As Ian said, yes, any EX flash (as far as I know) will work on both of your cameras.
...If I bump my price up to $ 225.00 will any other options open up for me that will work for both cameras? ...I would like something that requires little input from me
Well, that $87.00 Vivitar 285HV would work on both cameras, and it's pretty simple in auto mode: you pick one of four aperture ranges (pink, blue, red, yellow) based on flash-to-subject distance and zoom setting (approximately equal to your lens focal length), and then set your camera to the matching aperture. (There's a guide dial on the side of the flash that you set your ISO on, and as you zoom the flash it will adjust itself to match, and you just look at it to see which aperture matches the color you set on the auto sensor.)
It sounds more complicated than it is. Once you've done it once or twice it's simplicity itself. Anyway, once it and the camera are set you can shoot pretty freely from a wide range of distances, and it will automatically adjust the power up and down as you and your subject move.
That said, a more modern flash can set the output based on the camera setting with no input from you at all. $225 will get you a used 550EX right now:
or you can get a new Yongnuo 565EX for $160.00:
(I've never used them, so I can't recommend them, but I've heard other people say they work as expected. Same with Nissin; I've never used them, but I hear them being recommended by others.)
Lots of choices, depending on your wants and needs. Good luck with whatever you decide on.