Then it's not possible. Wait... is possible, you can try yahoo domain or domainarefree.com, even register.com however all of them renewals fee are high, Yahoo and register.com charge $34.95 for renewals fee, domainarefree.com charge $15 for renewals. In additional, all of them credit card are required.
There are some forums that offer free .com names if you reach a certain amount of posts. Google the terms forum and free domain and I'm sure some will pop up. You could also head over the the BST section of DP ... you'll probably find a .com going for an amount within your budget. .
Use this coupon code to register .com at GoDaddy: TEST99 Price = $0.99 + $0.20 for your first domain .com
I set up an account for a client and tried this. It did not work. In fact, it made the total go from $7.15 to $10.19 .
You can't register any .com names for $3, the cheapest is Name.com for $5.99 but I believe the prices goes up tomorrow!