You may consider another otpion which is https://www.skyairline.cl/default.aspx for flying to PUQ.
Much cheaper than LAN.
If you want to have a look at http://www.flyertalk.com/forum/trip-...via-h2-5p.html you will find more info about them.

Another option would to be to fly to PMC and then take http://www.navimag.com/_portada/index.aspx? to Puerto Natales . Great "cruise" with great landscapes, glaciers...