Add up the time you spend on all these competitions in therms of hours.
Look at the value of what you've won / grifted from your phone line.
There's no free lunches...
The cost of the time far out weigh's the cost of the items at the moment, but this don't mean squat to me in my little project.
Other 'pro-compers' as they like to call themselves say that on average they can make £2000 worth of prizes a month. From my little experiments with only online comps I can see this is indeed possible. The only thing this has cost me is time.
There are other types of comp's that can be entered that would increase my chance of winnings, namely ones that require slogans and well thought out answers. There is also a whole load of sms/phone text comps out there that can cost a fortune to enter.
Just because this time I have only won small prizes, don't mean I wont win something bigger in a future comp.
When it comes to the cost to time ratio, making a 'casual' computer game would more then likely make less money then pro-comp running!. Consider how many comps can be entered in, in the 6 to 8 months it would take to make a game.
At the end of the day its something I wanted to try in the past and now I have I am rather glad :)