You spend most of your day typing, so a solid mechanical keyboard makes work a lot less annoying and should easily last you five to ten years if you pick the right one. Instead of buying a cheap plastic board now and replacing it next year, we are aiming for a buy-once setup that feels great all day long.
Watch the release cycles closely because brands drop new models right before the fall semester starts, which is when last year's proven flagship versions finally get marked down. You get the exact same premium switches and aluminum build for a fraction of the launch price.
Just remember that the intro window is a deadline, not free money, and if any balance is still there at the end, deferred interest or standard rates will kick in hard.