A CDR Maidenhead - Paddington at £11.40, and a CDR Maidenhead - Newbury at £10.90 will cover you for this, but you'll need to be on a train that calls at Maidenhead. Unfortunately, Paddington to Newbury trains are usually non-stop to Reading.
So using the fast trains, you'll need a CDR Reading - Paddington at £18.10, then a CDR Reading - Newbury at £6.10, and a CDS Reading - Maidenhead at £6.00.
Thames Branches Day Ranger at £19.45 allows unlimited off peak journeys to from any station between Paddington and Reading, so that combined with a Reading to Newbury Off Peak Day Return at £6.10 is quite a bit cheaper. In fact with that combination the train doesn't even need to call at Reading!
It would need to call, because the TBDR is not a 'leisure travel pass' within the meaning of Condition 19, since it is not valid for at least 3 days in a period of at least 7 consecutive days. Personally, I don't believe that it would need to be a 'open' call for both picking up and setting down, but that is already being discussed on a different thread and opinion varies.