They don't come much cheaper than this model http://www.ebay.co.uk/itm/New-5V-8-Channel-Relay-Module-Board-for-Arduino-PIC-AVR-MCU-DSP-ARM-Electronic-/170745298865?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item27c1367fb1#ht_4006wt_1298