Sponsor your sister at a lesser cost...

You can sponsor your sister at a lesser cost, I just spent 100 QR for my sister's visa. The rest of the hard earned money went to her ticket.

Get a form from Qatar Airways, have it filled up (in Arabic), salary certificate or NOC, both of your passports and your ID, her certificate of live birth (serves a proof that you are related). Submit all of thist to the Immigration Department (open 24 hours) located near the airport. If you know the office of KEO there is a way there. There in 2 days time you can access her visa via the internet.

I hope this helps.

Goodluck!