speaker repair?

I don't think you understand the process on attaching leads on a sub. You take the lead material, which is longer than required, and solder it onto the voice coil wire. You then run it through the cone and pull it through the terminal hole, dress it properly, then solder them together. You are left with excess lead material through the hole which you cut off. Just because the person who made the sub didn't cut as much off one terminal than the other doesn't mean it is too short. The tinsel lead will be able to handle the full Xmech of the sub. That sub was obviously operating at that point for extended periods of time.

How much did you guys generally charged for a repair like that?

I can't remember. The best thing you can do is contact Infinity and ask them how much it will be.