I can highly reccommend the Aputure ones on ebay. They're much cheaper than any name brands and they often let you do more as they are more than just shutter releases. You need one that you can set the intervals so from the Phottix link below you would need the Nikos Digital, TR-80 or 90 by the looks. I have the equivalent of the TR-90 in Aputure (
http://www.aputure.com/en/product/di...te_shutter.htm) which was about $40 on ebay.
Of course if you have a high end DSLR it may be in built, like mine is. ;-)