I cannot tell you exactly how much the window is going to cost. The larger the window that needs to be replaced the more it costs.
Just a word of warning here: RV WINDOWS CAN BE VERY EXPENSIVE. The first place I would look is at the Replacement RV Windows Available on eBay. They seem to have the best prices on RV Windows. Most of the windows have "Buy It Now Prices" so you do not have to do any bidding. Amazon also has a large collection or RV Windows.
To answer your second question Yes, you can install the window yourself, just keep in mind that it takes two people to do the job right. The video below should help you understand how to do the job.
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