building low end gaming rig ,help me pick a psu

i dont know how to compute watts
this is my rig

Intel G3258
Sapphire radeon R7 260x 1Gb 0c
Gigabyte GA-H81M-DS2
G.Skills Ripjaws X dual 4GB (2Gbx1) 1600 CL9
caviar western 1Tb
? branded psu?
? cheapest Generic case ?

aerocool, CM, Corsair and hec are only available here. i want the cheapest but has the good quality

and if you want to know my budget for this rig
$400 without OS,ODD & Mon