https://www.harborfreight.com/power-tools/grinders/angle-gri...
(Cost plus a $30-$80 battery, of course, but after you pick your color, you've already got batteries). Your locks are far more protected by the social contract that would compel a stranger to stop someone who was cutting a bike lock with an angle grinder, and would cause a thief to fear arrest, prosecution, and jail time, than by actual physical security.
If you want a laser, you can already get a 100W CO2 laser tube for $500:
https://www.amazon.com/Cloudray-W2-Dia-80mm-Engraver/dp/B08G...
It won't do a great job of cutting steel - it will engrave it, but to cut steel you'd need O2 assist gas and a lot more power. It will trivially cut ABS, foam, fabric, wood veneer/thin plywood, cardstock, etc. if attached to a pair of mirrors on an XY stage such as might be borrowed/scaled up from a 3D printer. And, of course, it will trivially scar corneas with the invisible danger of its 10,600 nm laser light. Good news, though - ordinary polycarbonate safety glasses are opaque to the extreme IR light.
Laser safety is serious business, but highly-collimated, tightly-focused laser light is not likely to be produced by a cheap, portable laser. The above tube produces a 100W beam with a diameter of about 8mm. I wouldn't put my eyeball in the path, but a safety shutter can sit in the beam indefinitely and merely get warm. You melt steel by focusing a this 8mm beam down to a infinitesimally tiny spot, and beyond the focal length of your optics it diffuses to something no more dangerous than the source 8mm beam, and beyond that it's no more dangerous than an average lightbulb - albeit one that you have no aversion response/blink reflex to. I always wear my goggles near our cutting lasers, but I know lots of guys who have worked around 20W-20,000W CO2 lasers their entire lives and they're pretty cavalier with regards to laser safety.
Finally, a welding mask is a neutral-density filter, suitable for the (very approximately) black-body radiation produced by a welder, and is much less effective than laser safety goggles at blocking high-intensity light of a very specific color. Depending on the sensor, an auto-darkening mask might not even trigger when exposed to a laser! You'd want a set of 940nm laser safety goggles for this, which is far more exotic and dangerous than a 10um CO2 laser.