To address the original question: Where can you find a laser projector for less than $500? Well, it depends...

Most commercially-available projectors will cost quite a bit more than $500, because of the lengthy certification process (and the associated liability). I'm not familiar with the Canadian rules for lasers, but I suspect they follow IEC 60825-1 and 60601-2-22, which are very similar to 21 CFR 1040.10 and .11 that we have here in the USA. If you're buying a projector that complies with either of these standards, you're looking at spending more than double your budget even for a low power projector.

On the other hand, you might be able to find a supplier in China that could sell you a lower power projector for close to your $500 price point. GoldenstarLaser and OptLaser are both worth checking out. However, before you do this, you'll want to be sure you're not running afoul of any laser product import rules for your country. Again, I can't speak to the regulations in Canada, but the USA does have strict limits on who can import non-compliant laser products.

One final option is to build the projector yourself. This is probably the cheapest method, if you're willing to do a little soldering. If you want to try this, you might start by purchasing an all-in-one RGB laser module and a set of scanners from one of the Chinese suppliers linked above. Then you'll need a power supply to run the laser module (the scanners will come with their own power supply), and you'll also need a box to house everything.

You'll have to connect A/C power to feed the two power supplies, and then connect the DC outputs to the scanner amps and to the laser module. The scanner power supply will be a dual-polarity supply, usually +/- 24 Volts DC, so it will have 3 output terminals: Positive, Ground, and Negative. The laser module will probably run off + 12 volt DC, so just two output terminals (+12 V and ground). You'll also want to connect the ground from the laser power supply to the ground connection on the scanner amp power supply.

Then you'll need a male DB-25 connector (the ILDA connector) for the case. Connecting the signals from the ILDA connector to the scanners and to the laser module is fairly straightforward... Here's a picture that shows what each pin is for:

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Remember that the ILDA standard is for the male connector to be on the projector. You will only need to use pins 1 & 14, 2 & 15, 5 & 18, 6 & 19, 7 & 20, and 25, to get the projector to function.

The color signals go to the drivers for the laser module, and those inputs will be labeled on the driver. The X and Y signals go to the inputs on the scanner amps (which will also be labeled). Pin 25 is ground, which should be connected to the two power supply ground connections on the DC output side of each power supply. (Since you should have already connected the two power supply grounds together, you only need to connect pin 25 to one of them.)

Mounting everything on a thick metal plate will help ensure everything stays in alignment. Also, you may want to purchase an adjustable mount (MM1 or similar) with a first-surface bounce mirror attached to it so you can "steer" the output beam from the RGB module onto the scanner mirrors. Alternately, you can just mount the laser module so the beam is aimed directly at the scanner mirrors and then add shims under the laser or the scanner mount until the beam lands squarely on the scanner mirrors without the need to have the bounce mirror on an adjustable optical mount.