How do you haggle?

So the car we found is priced at $2995. The first thing the salesman said is, "Just want you to know, that price is firm. We bought it for $2100 and we put brand new rotors and brakes on. We can't go down on that price at all." Some see that as a roadblock. Others see it as a challenge. I'd personally like to see it as a challenge, but I'm not sure if I have the "cajones" to really haggle. Our mechanic said the car was sound, although it should have new tires. And he recommended we check the Kelly Blue Book value because he thought $2900 was a bit high. Hubby and I weren't sure what model this car was, so we did some "Hardy Boys-type sleuthing" and went up to the car dealership after they closed and used a flashlight to find the VIN number so we could check it out online. Turns out the Kelly Blue Book value is $2850 for the car in "excellent" condition. I say if it needs new tires, it's not in "excellent" condition. I say they've priced it $150 above the KBB value. I say we should offer them $2600. Of course, I say all that to myself. Now will I have the guts to say that to the salesman?