In terms of houseplants, yeah, cuttings are the way to go. The office and asking people you know is a good place to start.... but other than that, basically any public place you see a healthy plant, if you ask nicely to take a single leaf and have enough charisma... well, I wouldn't say no if I were the worker. The only place this isn't acceptable is nurseries, since that's their product, making it "proplifting" aka propagation+shoplifting.
A warning: Dirt just from outdoors/a hole in your yard is a great way to introduce pests into your house and diseases unto your houseplants. You can sterilize soil easily though, using a microwave, oven, boiling, or hydrogen peroxide. Then if you're using just some random dirt, most houseplants will need an additive like perlite or wood bark, and probably a fertilizer, to be their best. You still can't be sure that random dirt doesn't have some pesticides or other chemicals in it that will kill your plants... Personally, you're best off buying potting soil/sourcing leftover potting soil, not repurposing dirt. But if you just want to have "unkillable" plants like spider plants, ZZ plants, snake plants.... do what you want lol they'll live.
A very cheap alternative.... you can grow many plants in just water!
You can literally just get some spring onions from the store, chop off half the white part (and eat it) and put the greens in water, and they'll grow roots and more greens. Can be rather aesthetic in a kitchen window, and produces a source of never-ending green onions, just snip the tops.