You have 3 options. 2 of them require you to uninstall the window.
Option 1 is to get a new window complete, and install it. This is what the dealer will do, but what you save in labor will more than pay for any tools that you may need. The window may be available from Colaws RV salvage in MO.
Option 2 is to remove the window, buy the glass and dissassemble the window and install the new glass. This is by far the least expensive, but also the most time consuming. It also may not be feasable due to construction of the window.
Option 3 is take it to a dealer and write a check.
It all depends on you "DIY ability" the rivets are removeable with a regular drill. New rivets go in with a regular pop rivet gun. The rivet shaving is where the tool gets expensive. $170-190.00. If you stay in the Airstream community you will be everyones best friend if you have a shaver.
You can knock the rivets down with a dremel tool, but shaving will make it look OEM. If you go the dremel tool route I reccomend just getting the mandrel and top of the rivet knocked off, then when you make freids with a shaver owner you can shave them off.