best practice for use of functions..

My application does between 20-40 inserts per transaction.  I am putting all
of them into functions to limit the calls from the DBI to the database.

My preferred method is to have a function for each table that I do an insert
into, it's easier to manage that way and a lot easier to make changes if I
add/drop columns and tables.  Right now I have one function that is called
by my application that in turn calls all the other functions.

I am wondering is there is a significant overhead for calling say 10
functions from within a function compared to putting everything into one
single function?  Or are there other reasons why I would want to do it
differently?

Chris