Can anyone suggest a budget priced hotel within a short walk of the Sidbahnhof?

Does it have to be within a short walk? I ask this only because the Sofitel Vienna is a very common Priceline 4* choice that people often get for under $100 and it's a block from a stop on the D tram that will take you directly to the Sudbahnhof. The tram ride to the station from that stop is only a few minutes.

Other than that, I can't think of any offhand. The Sudbahnhof area isn't my favorite part of Vienna although admittedly I don't spend much time there. Perhaps Molker will have some better suggestions. Anyway, you might want to try Priceline if you can't find anything. And what exactly do you mean by "budget"? Under 100 euro, under 50?

Make it by the Westbahn, and you can stay at the Fuerstenhof:
http://www.hotel-fuerstenhof.at/default.htm
Great place right across the square from the train station.

The Prinz Eugen hotel is across the street from the Sudbahnhof.
If you just need a place to sleep for one night near the station, this 3 star is OK - mixed reviews.
If you stay longer in Vienna, as BTilke advises other better hotels available near to the streetcar " D"

Hotel am Schbertring is one such places about 3-4 stops from the station at Schwarzenberg Platz

Yes, that's the same stop near the Sofitel, although I think the Hotel am Schubertring is closer to it. However, I think you can get the Sofitel for less, esp. if you Priceline.