If the aliens are robotic/electronic in nature (perhaps having long ago replaced their biological predecessors), long timescales may mean nothing to them. Simply go into 'sleep mode' until the ship arrives. Or not ... a robot might have no concept of 'boredom' and no problem remaining fully conscious for however long it takes to slowly cross the distance.

If the aliens naturally have very long lifespans, they may view a travel time of 500 years as 'reasonable' for such an important voyage.

If they have some sort of 'hive mind', where a large group of them can consider themselves a single individual (or even just a very collectivist culture), then they may see no issue in crossing interstellar distances in a 'generation ship' where only the eventual descendants of the original crew will reach the destination.

If they've perfected some sort of anti-aging technology and/or the ability to freeze themselves in stasis, they might see a long travel time as relatively unimportant. If they live indefinitely long and are already thousands of years old, what's a few hundred years of spaceflight? If they can freeze themselves (literally or figuratively) and wake up when they're about to arrive so that the subjective travel time is only a few hours, they may see that as worthwhile.

would require more energy

... if done by any technology we know or could dream up with our current understanding of physics.

But we already know our understanding of physics is fundamentally incomplete. We don't know what dark matter or dark energy are. We don't have a reliably working theory of quantum gravity. We haven't managed to join quantum physics and relativity together yet in any functional way.

It's highly speculative, of course, but we can't rule out the possibility that aliens with a better understanding of physics might be able to develop a way to travel at extremely high speeds without needing as much energy as our current physics suggest it would require.

The amount of energy required also greatly depends on the mass of the ship making the journey. It's possible they could reduce the energy requirement by miniaturizing their spaceship. Say, a very small robotic probe capable of self-replication, and carrying blueprints for building more macro-scale technology and possibly rebuilding the aliens themselves. The tiny spaceship can then be accelerated to very high speeds with relatively little energy. When it arrives (say, on the far side of the moon), it can then harvest local resources to replicate itself into an army of builder bots, and then use more local resources for those builder bots to assemble a proper alien ship/base, complete with aliens inside. With this strategy, all you need to carry is enough machinery to build a copy of the probe + data storage to contain all the blueprints. Conceivably, that could all be achieved in a very small package, perhaps even microscopic -- after all, self-replication and data storage are things that microscopic single-celled organisms can do on earth. In theory, there's no reason a microscopic robot couldn't do the same things. You could achieve extremely high velocities with relatively little energy if your spaceship was, say, 1cm in diameter and weighed less than half a gram.