Quantity   Component name
1 × Mains electric cable with plug I have bought a cable `1.7m 3x1.5mm2` with plug for about 2$.
1 × Outlet Box with 4 sockets, switch and grounding I had a couple of them lying around after buying a year ago in local store. The model I used called BR-1564-0 http://en.borsan.com.tr/urunDetay.aspx?mod=118. The price is up to 4.50$.
1 × ESP-01 (ESP8266 module I have bought ESP-01 about a year ago, now you can buy a better and cheaper version http://www.aliexpress.com/store/product/Free-Shipping-ESP8266-remote-serial-Port-WIFI-wireless-module-through-walls-Wang/110055_2038015597.html, the price is 2.18$.
1 × Arduino Pro Mini I have bought a dozen of cheap clones of it. You can buy it here: http://www.aliexpress.com/store/product/2pcs-lot-New-Pro-Mini-atmega328-5V-16M-Replace-ATmega128-For-Arduino-Compatible-Nano/110055_1039035704.html for 1.75$.
1 × 2-channel Relay Module can be bought here: http://www.aliexpress.com/store/product/With-optocoupler-2-channel-2-channel-relay-modules-relay-control-panel-PLC-relay-5V-two-way/110055_1672127426.html for 1.66$.
1 × 5V Power Supply Again I wanted something small and easily achievable, so I have repurposed a cheap USB power supply called: "Travel Convenient EU Plug Wall USB Charger Adapter For Samsung Galaxy S5 S4 S3 Note 3 Charger 5V 2A". Of course, it will not pass even smoke test on >0.6A output current, but it work ok with 0.4A load. I have bought it here: http://www.aliexpress.com/item/Travel-Convenient-EU-Plug-Wall-USB-Charger-Adapter-For-Samsung-Galaxy-S5-S4-S3-Note-3/32220133044.html for 1.16$.
1 × LM1117-3.3 voltage regulator (or another like LD33 that can create 3.3V from 5V), two resistors for about 10k each, one electrol In total about 0.2$.
1 × 2 M3x10 countersunk screws, 1 M3X10 screw, 3 M3 nuts, 4 M3 washers, 3 M3 lock washers. I guess about 0.1$.
1 × ABS plastic, solder, rosin, low voltage wires, mains wires, a piece of kapton, narrow heatshrink. About 1$.