Admission to the El Jem coliseum is really cheap: just 10 Tunisian dinars, or just over 3 euros. As an added bonus, the El Jem archaeological museum is free to visit on presentation of the coliseum entrance ticket! The two sites are less than 500 metres apart.
You can't buy tickets online, but you can find contacts and information on the museum's official website, which even offers a virtual tour! The museum is open from 8am to 5.30pm (until 6.30pm from 18 July to 15 September).
Every summer, El Jem plays host to the International Festival of Symphonic Music, held in the almost 2,000-year-old amphitheatre, a unique opportunity to enjoy a concert in the prestigious Roman theatre, a UNESCO World Heritage Site! El Jem is the only city in the Arab world to organise a truly international festival devoted to symphonic music. There is no official Coliseum website, but thereis a website dedicated to the festival, where you can book your tickets for the festival.
The nearest airport is Monastir, 70km away, a one-hour drive. If you are staying in Mahdia, the transfer takes just 40 minutes.