1. Vienna to Salzburg (Return) - would it be better to purchase a Sparschiene ticket or the Einfach Raus ticket
Well, Einfach-Raus-Ticket is valid for one day (+ only from 9am on weekdays) and journey by regional trains (you can't take InterCity with Einfach-Raus-Ticket) till Salzburg will take at least 5 hours one way. So it might be not really manageable to do a day trip Vienna-Salzburg in one day with Einfach-Raus-Ticket. While discounted Sparschiene tickets bought from
OeBB ticket shop (not sold at the station) start from only 19 euro one-way, making it 38 euro return, but spending 3 or even less hours one way. Also you might not bother with any ticket prepurchase in advance, but just use instead
WestBahn, their full fare Vienna-Salzburg tickets cost almost the same as discounted OeBB
2. Vienna to Bratislava (Return)
Easiest leg, since you can just buy at the station EURegio return ticket Vienna-Bratislava for 14 euro, it will be valid for 4 days and in addition even include 1 day pass for Bratislava city transport.
3. Vienna to Budapest (Return)
Here you have few options to consider: a) buy in advance (meaning right now) discounted one way 19 euro ticket Vienna-Budapest via OeBB Ticket Shop (we have a
guide on how to purchase such tickets), then do the same, but opposite way - Budapest-Vienna for 13 euro (yes, the opposite way discounted tickets are cheaper) via MAV website, again
our guide on how to do it; b) if you don't have any fixed date or time you want to travel (will be require with option 'a'), then you can take advantage of EURegio tickets from Vienna to Hungary: for instance Vienna-Gyor return EURegio ticket (again 4 days validity) cost 19 euro, while in Gyor you just buy domestic Hungarian ticket Gyor-Budapest (from 2520 HUF one way), same idea on the way back - ticket Budapest-Gyor + return part of your EURegio Vienna-Gyor. But remember that with EURegio tickets you won't be able to use high-speed RailJet trains, but instead a bit slower regional ones; c) OeBB offers special so-called 'Excursion' ticket to Budapest from Vienna, it cost 39 euro, also valid for 4 days and can be bought online from OeBB Ticket Shop, although as you can see, option 'a' will give you better option with the same conditions.
Also in case you don't plan to spend long time in Bratislava or Budapest, then we have an idea how you can save even more. Trick is to do the trip following way: Vienna-Bratislava-Budapest-Bratislava-Vienna. In a case of such scenario (and <4 days) you will need just EURegio Vienna-Bratislava for 14 euro and return ticket Bratislava-Budapest (17,5 euro, can be bought any time). As result you can visit both Bratislava and Budapest for just 31,5 euro
Are Sparschiene tickets available at train stations in Vienna or do they have to be purchased online only?
Sparschiene tickets for domestic routes are sold only online, while for international ones you can buy them at the station, but again since those are in limited number, chances to catch any discounted Sparschiene at the station ticket counter few days before departure are minimal, most of them will be already sold out
Where can I purchase the EURegio tickets? Online or at the main station in Vienna (Westbahnhoff?)
Just buy it at the station. Fare for EURegio tickets doesn't depend on time of purchase, plus anyway you can't buy them online
I plan to do Vienna-Salzburg-Werfen-Salzburg-Vienna round trip in one day. The Einfach Raus ticket is quoting Euro 28 while the best Sparschiene available is Euro 86 (return for 2). I was just wondering whether the Einfach Raus ticket will cover the roundtrip from Vienna to Salzburg and back to Vienna for 2 people.
Yes, Einfach-Raus-Ticket will cover it and Salzburg-Werfen leg as well. But as was noted above, you need to take into account that traveling by regional trains is a bit slower, so Vienna-Salzburg-Werfen-Salzburg-Vienna in one day will be possible, but might mean spending almost all the time on the road