What are the considerations when using SERLIALIZABLE over READ COMMITTED isolation level in Oracle?
Is there any extra cost associated with, for example, having to go potentially further back in the undo data to return the records?


Example:

You have a table getting one insert every minute.

If a SERIALIZABLE transaction started at 4:00pm, and queried that table at 4:15pm, then it will have to read at least 15 undo records to return to the state of the table when your transaction started. If there had been no activity on the table, then there would be no additional workload. 

Ultimately it would depend on how long the serializable transaction last, and what changes are made to the data it looks at during that time.

I'd add that it is rare to see SERIALIZABLE used. The same mechanisms support DBMS_FLASHBACK with the advantage that you can specify the exact time for which you want to view the data (eg Closing balance at 5pm).