Short answer: The $4 tier is the most expensive on TenDollarPick: Paris, London, Rome, Milan, Monaco, Edinburgh, Reykjavik, Tel Aviv, Lucerne, Interlaken, Bergen, Tromsø, Nice, Queenstown, Honolulu, Ibiza.
TenDollarPick rates cities by $10-day feasibility. The $4 tier is the hardest — base cost alone is 40% of your budget. Even at $4, a $10 day is possible: dorm bed ($1) + street food ($1) + walking ($0) + free landmarks = exactly $10. But it's tight. Most $4-tier cities are Western European capitals, Nordic, or famous resort cities.