Coolant loss after replacing CV axles

[wirez]

Hey guys,

I'd better mention that I don't have much knowledge about cars.

I put my 02 Boxster S in a shop for 2 weeks to replace CV axles and for other issues; checking brake sensors and finding the source of minor oil leak.

Although they replaced the CV axles, they said they could not find any problem with the brake system. For oil leak, they only adjusted oil filter housing. (I don't think that doesn't create dusty oil residue all around parts that I can see from under my car.)

Here are my questions;
1. I was wondering why coolant level went down below lower limit. (The level reached up to Max level when I did oil change two weeks ago.)

2. How much does a pair of CV axles cost?
They charged me $1,100 for the parts only but I expected it would cost more than that. Did they really use genuine parts?

3. Is there other possible/reasonable cause of oil leak of my case?

Thank you in advance.