Rennes Airport is just to the south of the city, but is a small-ish airport with connections mostly from within France. From the airport, the line 57 bus leaves every 30 minutes, taking 18 minutes into the city centre and costing €1.
Alternatively, Nantes Atlantic Airport is further away but is a large, international airport. Buses from the airport leave every 10 minutes into the centre of Nantes – the journey takes 20 minutes and costs €1. From Nantes, trains to Rennes leave every 2 hours and take 1 hour 30 minutes. A one-way ticket will cost around €20.
Each individual show will have different timings, depending on venue and day. See each billing for specific details.