I was about to send an e-mail on train tickets
As Grahame says - you can pick up a return for eight quid on Southern. You can even book from Darsham, although you can't book a bike space on the Darsham to Ipswich train. If I were coming back I'd book on the 16.49 from Darsham.
The ride to Ipswich is nice, although I'd be tempted to go via Saxmundham and Woodbridge, which is about 34 miles.