Salar De Uyuni 4D/3N tour

Hi,

My wife and I are planning a visit to Salary De Uyuni this August, from San Pedro and returning back to San Pedro. I have contacted 3-4 operators for private tours with the "luxury" accommodation options like Palacio De Sal, Mallku Cueva etc. All of them have quoted $1200-1500 USD per person for a 4 day 3 night private tour. I wanted to get opinions on

1. If this is a fair price considering that we would need to book in advance to get these hotels or can we still get these hotels if we go there and book a couple of days before our tour?

2. And is a 4D/3N trip better than a 3N/2D trip considering that we are returning to San Pedro?

Looking forward to suggestions and advice.