A common, well-tested pattern for three-tier pricing is roughly 1x / 1.7x / 2.8x the base price. The middle tier is usually the one most clients pick, it should feel like the obvious best value, not just "more expensive." The top tier exists partly to make the middle tier look reasonably priced by comparison, and partly to capture the clients who want the most you offer.
Once you've set your numbers, list 2-4 concrete things that differ between tiers (turnaround time, revision rounds, deliverable count, support level) rather than just changing the price, clients pick based on what's included, not the number alone.