To cut a deal means to get a discount.

Since there are idioms similar to because, Seeing as how is one that have a meaning similar to ; since. In this case it is used to introduce the reason he thinks he should have a discount, which is that the person doing the job used to own the vehicle.

To get to rock bottom means you have reached the lowest point in your life and not high. When you dig in dirt you hit a rock. You can’t go any lower. What do you think of Shawn Spencer?