As two of the previous posts mentioned, you also want to make sure you use a 20 amp circuit. Electricians, please correct me if I'm wrong, but I believe you don't want to exceed about 80% of your amperage rating, so that would be around 16 amps on a 20 amp circuit. Just something to keep in mind in case you have additional things plugged in on the same circuit.
I have a HERMS using two 1500 watt elements (one in heat exchanger, one in HLT) each plugged into a dedicated circuit. The only 12 AWG cords I could find at Lowe's were the ones intended for window AC units. I can't remember how much I paid, but I want to say they were around $12 each.