You want a machine that handles heavy frames and stays fast for the next five years, which means buying once instead of settling for a mid-tier compromise. A top-tier rig usually costs about $2000, so you want every dollar to work hard and last.
Watch the manufacturer release cycles closely. When the newest chips drop every spring, last year's flagship model immediately gets discounted, giving you the exact same build quality for hundreds less.
That intro window is a firm deadline, not free money, and any balance left when it ends will trigger standard interest charges on what is left over.