The best restaurants in Rimini are listed in the Michelin Guide: Lazaroun (located in the historic centre and specialising in traditional Italian cuisine), Lo Squero (seafront and renowned for its seafood), Ristorante Guido (nestled right on the beach and boasting masterful fish cooking).
Prices in prestigious restaurants in Rimini are a bit "bite": a dinner for two can easily cost 200 EUR, but not all dishes are expensive (you can have a nice dinner for 50-60 EUR).
By the way, inexpensive restaurants in Rimini also offer tourists a good choice of dishes and their quality. For example, the average bill per person in the restaurant Da Lele is 15-20 EUR, and the institution itself has excellent reviews.
Carlos Restaurant, while not boasting the lowest prices, is popular with tourists for its large portions and variety of dishes.
Rimini's Chinese restaurants are not bad: you can eat here for less than 10 EUR.