You want a desk frame that lasts years, not months. Focus on dual-motor models that handle your monitor weight without wobbling. If you buy a solid frame now, you can just swap the desktop surface later if your style changes.
January is the best time to shop because office furniture retailers clear out old inventory. Look for last year's model, which is often identical to the current one but marked down significantly once the new versions hit the floor.
Remember that the 0% intro APR is a temporary offer, not a permanent lack of interest. If you haven't paid off the $350 balance by the end of the 15 months, the remaining amount will start accruing interest at the standard rate.