I am not sure if this have been covered here but:

You can get the SF weapons without purchasing the game. In fact you can even get more unlocks.

All you have to do is have someone with SF log on as you and then play a SF map. Then leave, and log ing again. Bam. multi unlocks and SF weapons to pick from.

It works, I did it for one of my friends that could not afford SF.

Sorry, if this has already been posted.