The four bags of Reese's cost $9 x 4 = $<<9*4=36>>36.
The three bags of Snickers cost $5 x 3 = $<<5*3=15>>15.
The five bags of Skittles cost $7 x 5 = $<<7*5=35>>35.
Therefore, the unicorn piñata and the treats cost $13 + $36 + $15 + $35 = $<<13+36+15+35=99>>99.
#### 99