Data Recovery for Accidentally Erased Hard Drive
There is a product called DiskDrill that I have used with good success.  You can use the product for free to see what it can find.  To actually recover your files, you will need to purchase a license.  

The key to a successful recovery is to immediately stop modifying the drive.  You either need to get a new drive and connect your original drive via USB, or boot from external (USB) drive and run the recovery utility.  The more you modify your drive, the less chance of recovery.

My suggestion is now is a good time to get a new SSD and convert that older drive into an external USB so you can create an image (through DiskDrill) of the drive for recovery and then when you are done, set it up as a time machine back up.  A USB to SATA adapter can be had for less than $15 so this is a very cheap option.