I bought a pistol two weeks ago. I forgot my lock so they let me borrow one. I walked out to my car, dropped off my pistol, and then gave them back their lock. Saved me $25. That's how it should be done.
That said I've had some experiences where I was required to purchase a lock from the store. One time I don't think the lock was ever even mentioned, I just signed and walked out...
IF...the handgun is used and manufactured before 2003, an internal lock is not required. A cable lock is still supposed to be supplied and we will give you one if we have spares. The internal bore locks are more expensive, however, and we can't just hand them out for free. We could build them into our firearm prices, but then you would be comparing our price to someone who doesn't. Also, why sell one to someone who already has one or perhaps more.