You won't find one nearly that sensitive at the HD. You're going to have to go to specialty electronic supply place or order on online. Plan to spend at least $300. Not worth it is it? Ground right to the battery. Don't need a DMM to measure that resistance; I can look it up on a table. Wire for that is going to be much cheaper than the DMM.
Aren't going to find one there either. You need accuracy on the order of 0.001 ohms. Gonna cost you and they aren't common for the simple reason that the vast majority of users don't need that level of accuracy.