Sorry to break it to you folks! Unlock codes normally do not come free. There are occasional promotional offers that some companies put up for free unlock codes. You can try to wait for those, but I've only seen a couple in the past few years.
The downside to that is that because you don't pay a cent, your order is not given any type of priority. I remember when a company was giving away free Blackberry unlock codes for a week, there were some people who didn't get their unlock code for a few weeks when they're processed anywhere between instantly to a maximum of 24 hours.
Regardless, if your budget is tight, and you're not willing to pay a nominal fee for mobile freedom, I'd recommend waiting. Of course, if it is a rush order, you'll more likely have to pay your dues and take it as it is. Everyone needs to make money in some way, shape or form.
Best of luck!