For
Salzburg-Prague trip there are three obvious train options:
1) easiest is to purchase discounted tickets from Austrian railways website (now there is simply no chance to make mistake there
). Those start from 39 EUR per passenger. But the connection they are offered for is 14:10 from Salzburg and 20:40 arrival to Prague.
2) purchase already mentioned Einfach-Raus Ticket, it will allow you to travel from Salzburg all the way till Austrian-Czech border (Summerau-Horni Dvoriste), then you can purchase online ticket Horni Dvoriste-Prague (412 CZK for two of you -
https://www.cd.cz/eshop/search.aspx). And the beauty of this option is that you don't need to get off train on the border, because most of the trains from Austria go all the way till Ceske Budejovice. As result you can make it to Prague with only two train changes (in Linz and Ceske Budejovice) while paying 28 EUR+412 CZK.
For instance, there is a nice morning-afternoon connection - depart Salzburg 8:39am (REX 3013), arrive to Linz 10:57am, depart from Linz to Ceske Budejovice 11:14 (R 1932), in Ceske Budejovice you at 13:43, depart Ceske Budejovice 14:04 (R 648) and arrive to Prague at 16:40
3) you can actually go from Salzburg to Prague via Germany as well. There is a similar to Bavaria ticket day pass, but it is valid till neighboring with Bavaria Czech regions. It is called Bavaria-Bohemia ticket, cost 34 EUR for group up to 5 passengers and can get you from Salzburg till Plzen. From Plzen to Prague you will have to purchase Czech domestic ticket (216 CZK for two), but as in previous case you won't need to get off train in Plzen if you prepurchase your Plzen-Prague ticket in advance and print it on your own.
For instance, in such way you can start you journey from Salzburg either at 6:09am by direct train to Munich or 6:24 with one change, both options will get you to Munich before 9am, depart Munich by ALX 355 at 9:01am and arrive to Prague 14:54. Similar connection available for the afternoon-evening also