A high-end mechanical keyboard is a tool for life. It makes typing less of a chore and saves your wrists. If you buy a solid aluminum deck now, you won't have to replace a cheap plastic one every two years.
Black Friday is the best time to buy. Tech brands usually release minor updates in the fall, so last year's flagship becomes the smarter buy. You can get top-tier build quality for about $250 and keep it for a decade.
The 18-month window is a deadline, not a suggestion. If you still have a balance when the 0% for 18 months on purchases and balance transfers from date of account opening ends, the regular interest rate will apply to the remaining amount. Pay it off early to keep the cost at $250.