What are the business goals?
Do you need replication or backup? Is this a selling or technical issue?
WIll the replicated data just seat there as a backup or will they be used in parallel with the source data?
You should talk with the customer to find out what they really need. Snapmirror is not too expensive and is very useful. They will not regret it.
For replication and since it is files you can use robocopy or rsync (for Unix). Setup a schedule with robocopy with the proper options (logically /MIR).
What are they using currently for backup?