On a budget, Antibes still earns its price.
Train ~€5 each way; Picasso museum €8
Arguably the most well-rounded Riviera day-trip: an atmospheric walled old town, a covered Marché Provençal, the cliff-top Picasso Museum in the Château Grimaldi, the megayacht-lined Port Vauban, and actual sandy beaches. It's lower-key than the headline towns; the catch is the most charming bits (Cap d'Antibes walks) are spread out and need time or a car.