Bit of detective work with the fares you've quoted suggested Advances (ADV) on the 1455 FGW HST from Bristol (changing Plymouth and Par) on the 25th and the 1722 from Newquay (changing at Par) on the 30th July.
If those are indeed the trains you looked at then instead you can buy an ADV on the 1444 CrossCountry as far as Plymouth for £18.00, an Off Peak Return (SVR) between Plymouth and Newquay for £11.80, then taking the 1722 on the 30th from Newquay (change at Par) using the return portion of the SVR. Then an ADV from Plymouth on the 1942 (which is the train you'd connect into at Par) for £16.00. Total £45.80
There another cheaper option with ADVs splitting at Plymouth if you leave Bristol earlier (0828 ) on the 25th. Involves a 2 hour-ish wait at Plymouth and would involve travelling on an all shacks DMU as opposed to a XC Voyager or FGW HST. £13.50 ADV on the 0828, arrive Plymouth 1112. Then £3.00 ADV on the 1334 FGW HST direct to Newquay. On the return you can get a £3.00 ADV on the 30th on the 1722 from Newquay to Plymouth (changing at Par), then staying on the same service using the £16.00 ADV from Plymouth to Bristol. Total £35.50
Bear in mind the ADV prices are quoted as correct at the time of this thread post and are subject to change.
