AFAIK, there aren't any sub-$100 ready-to-shoot Infrared (IR) triggering systems which won't require at least cutting and soldering an electronic cable release.
But if you can manage that much, there are any number of miniature IR triggers available for industrial purposes that should fit the bill.
I'm a big fan of these, they're waterproof with a 35' range and have very low power requirements:
http://www.enforcer.com.tw/burglar/E931S35RR.htmGot this shot using two of them, in a crossed-beam array:
http://www.ivaneberle.com/P.concolor9.htmlI find these better than the Dale Beams of old or their modern equivalents because they're much smaller, and can be concealed better. As well, two triggers with beams crossed is a huge advantage for good composition and that your subject will be in the frame (defines a point in space when both beams must be broken simultaneously in order for the camera to fire), and eliminates false triggers from mice, etc. This doubling down rapidly gets to be outlandishly expensive with Trailmasters, Dale Beams, Kaptures and the like especially if you have multiple sets going at once.
Back in the old pre-internet days, many of us were consigned to using the $40 Radio Shack 49-551 triggers because they were cheap and easy to source. But they don't make these anymore and they needed to be modified for dual trigger arrays, anyway. If you can find one or more of these they might still work okay for digital because it won't matter as much if you waste frames with the 3 second lockout feature they come with (also many years ago I discovered how simply disable this feature by removing a capacitor).
Your digital camera or even relatively modern film SLR can be a power-hungry weak link. Waking up your camera long ahead of the actual triggering in order to charge the flash capacitors is the challenge, at least for long-term sets without the manual intervention of swapping out batteries every six hours or so. I haven't used Canon gear so I can't say for sure how this will work for you, but if your camera enables waking up the (cabled) flash from sleep with a half-depress, an motion sensor can be adapted and added to the array just for this task. Things start to get somewhat complicated electrically, here so you might be best advised to try it incrementally by swapping out camera and flash batteries every few hours to start with. Or, you might be well served to try all this with manual film cameras with little or no battery dependence (my old Pentax LXs are good for this) and flashes that will remain powered up by themselves. (Many are so cheap today as to be near-perfectly suited to the task.)
I have a Quantum Turbo 2x2 that I use to power everything, and recycle a flash capacitor in 1s from a full power pop. I house all of this in a Pelican 1450 case that I've cut portholes in. The lens is protected by a UV filter and weatherproofed by folding a rubber lens hood back flush with the case.
Ivan J. Eberle