Vegas is the loudest pick and the most expensive one. About 300 hotels in the city are 18+, and almost all of them are off-Strip — the casino flagships default to 21+ and don't make exceptions. That means Sonder, the budget-mid Holiday Inn Express tier, the Boulder Highway strip. You can still do Vegas at 19; you just can't do the headline resort. Aim for Sunday through Wednesday in the back half of May and you'll save real money.
Florida is where most grad trips actually end up, because it's the deepest 18+ market in the country at 5,742 hotels statewide. Orlando alone has 1,325 — the largest single-city pool we track. The mid-tier Orlando properties off International Drive run somewhere in the $90–140 range a night even in peak May, which is roughly half what you'd pay for the same room class in Vegas. Miami and Hollywood are the beach options if the parks aren't the vibe.
Myrtle Beach is the budget play. 501 verified-18 hotels in the city, with another 332 in Conway 10 miles inland. South Carolina has the highest 18+ share of any major beach state at 86.1% — basically every hotel along the coast is willing to take you. For a group more interested in a beach week than a club week, Myrtle gives you the same energy as Florida at maybe half the Vegas room cost. Six people in two adjoining queen-doubles often comes in under $200/night per room.
Nashville is the third reliable pick and probably the most underrated. 777 verified-18 hotels in the city, with Lower Broad putting you walking distance from the bar circuit, the Ryman, and the food. Catch: none of the bars are 18+ — Tennessee runs 21+ for entry, so half the strip is off-limits if anyone's under. But the hotel side is fully solved, and for a group that wants live music and food more than a club night, Nashville beats Vegas on cost and rivals Miami on energy.
About the money. Every hotel holds $50–200 a night against the cardholder's card for incidentals, on top of the room rate. Four nights means up to $800 sitting in limbo, released a few days after checkout. If you can use a credit card, use one — debit holds freeze real cash that could collide with your gas, your food, or the bar tab everyone owes back. A grad trip is exactly where a stuck $600 hold becomes the problem that wrecks the last day.
One thing every city on this list has in common: you can't drink in the room. Federal law is 21 anywhere in the U.S., and front desks do welfare checks when neighboring rooms call in noise. Getting caught is an immediate eviction with no refund, even on a non-refundable rate, plus a cleaning charge. The 18+ check-in policy doesn't change that. Keep the party out of the room and you keep the room.