River cruise is 3.80 one way 6.50 return. Cheaper to get a saveaway think they around 4 quid.
Except you can't use Saveaways on River cruises; you also can't use them until after 09:29. Which essentially means, you can only use them on the 09:40 direct departure from Seacombe, and then between the hours of 16:15 and 19:05 on the evening direct commuter services.
A saveaway is great value if you are planning on doing a lot of travelling/if your total ticket cost works out higher, dependent on the times you want to travel, they are £3.30 for a single are and £4.50 for an all-area's pass.
You need an all-area's saveaway if you wish to use it on the ferries.