You want a dual-monitor setup that actually makes working from home less painful and lasts you through a good few years of desk duty. Buying the right gear once beats replacing cheap screens twelve months from now because the colors washed out or the stand wobbled.
August is prime time for back-to-school sales, which means retailers drop prices on monitors to clear out inventory. Look for last year's monitor models right now since they get deep discounts when the newer versions drop, and they usually offer the exact same daily performance for a lot less cash.
Remember that the intro window is a deadline, not free money, and any remaining balance at the end of the 18 months will start accruing standard interest.