data recovery

I don't know that Apple will offer to do data recovery at all.. What have you lost and from what system (hardware)

If it's a single disk system then looking at the excellent Disk Drill from CleverFiles is a great program. Ideally you'd want to boot from an external drive/usb key and run disk drill pro from there and recover the files to an external drive rather than the volume you lost them from. Disk Drill does have a trial version which if it finds your files you can purchase it after to do your recovery. I just managed to successfully get 1.2million files back from a failed lacie drive for a client.

Beatle

You do have chances to get back your data, provided that you've not write anything else there since then. Any new data would rewrite your inaccessible data and erase it forever.

Therefore, you should take care not to use your computer till you are ready to restore your data back.

As everyone writes, in order to restore your data back, you need data recovery software. There are plenty of data recovery programs that could easily retrieve inaccessible data. You are supposed to select a most suitable one.

I hope you could learn a lesson to back up all your important data in the future.