This site will give you an estimated cost of running the lamp, but you will need to know the Watt rating of the lamp, how long it will be on for each day and how much per Kwh you pay for your electricity. (You can find the Kwh cost on your last electricity bill). http://www.justlocal.com.au/clients/energy-cost/" onclick="window.open(this.href);return false;
Thing to keep in mind Nathan is you are not actually paying the bill ,your parents are .
I would not allow it if you were my child , power bills are just too high as is .
Accept that some days you are the pigeon, and some days you are the statue.
David Brent
Forget about a power point in your case,run a lead to your aviary. Buy a heat lamp and trial it first with the power lead, suitably positioned not to get ran over with the mower.Then wait for your parents to get the next power bill and see if they noticed any difference,If they don't notice any difference in power consumption it wont mater, If they do you will get the blame anyway even if its not the lamp.
VERY IMPORTANT NATHAN.... have your folks check that the lamp is in a suitable position and correctly installed not to burn the place down before turning it on.