I've put the Fenris Arena missions seperately because they become available at odd points during the game depending when you start them (I think it's based on how many missions you complete between each round, but could be wrong.) All Arena missions are hired by The Fenris Arena, in the Frontier region. You aren't permitted a wingman for any of them. None of the missions unlock any weapons, ships, etc.

There are six opponents for all but the bonus round.

Arena Qualifier Round 1 (250 cr. - Darts)
Arena Qualifier Round 2 (500 cr. - Makos)

Arena Tier 1 (1000 cr. - Piranhas)
Arena Tier 2 (2500 cr. - Shrikes)
Arena Tier 3 (5000 cr. - Nighthawks)
Arena Tier 4 (10000 cr. - Mantas)
Arena Tier 5 (25000 cr. - Gars)

Bonus Round (50000 cr. - Demons x 4)

Grand total: 94,250 credits for all 8 missions.