We could get THERE right now. It would take a huge effort, but such a craft was proposed decades ago using propulsion powered by atomic bombs. Project Orion if I recall correctly.
Imagine a civilization like ours facing planetary destruction for some reason. Or they’re just expansionist or it’s a splinter pirate group, whatever. They send a generational mission, or one with suspended animation. Or a robotic advance guard. There’s no need for Independence Day highly advanced capabilities.
The thing is, I see it this way: Technology is advancing so fast that even someone only “slightly” more advanced than us would have a field day with us. And like you said, it would take a huge effort, meaning they are “desperate”.
If they have the technology to get here even remotely reliably, they are way ahead of us.
Remember the movie “district 9”? My interpretation of the end was that the human race was a dead species walking once that ship escaped.