We took our RV through Austria to Italy a couple of years ago and obtained a go box,
as we are over 3.5 tons, if you are 3.5 tons or less you need a vingnette.
Where we picked ours up they set the box up, asked where we were going and put enough money on it to get us there and back, we returned the box to the same place and got a refund. Before going we had asked questions, looked at web site with people saying how difficult it was, it wasn't it was a piece of cake.
We have been across Austria quite a few times, twice last year. The box costs 5 euro then you put cash on it. The minimum is 75 euro. To give you an example we travelled through Austria into Slovenia on route to Croatia, we used the main autobahn all the way and the approx cost each way was about 75 euro each way. I am a tag axle at 5 ton. The charges are also related to the emissions, I am Euro 5 so that is cheaper than say a euro3.
If you are Euro 5 then be warned that you have to send your certificate of conformity showing you are euro5 to Asfinag in Austria (I did it via email and copies) within 14 days after you leave. The first time we crossed in a euro5 in April last year I didn't do it. When I went through again in July they pulled me over and fined me 100 euros. They had also reduced the euro rating on my go box to euro1. After I paid they returned it to a 5.
It is quite easy to get the go box at the service stations prior to entering Austria, you will need your vehicle registration docs.
if the box beeps 4 times..............you won't leave Austria without a huge fine.
if the box beeps 3 times (iirc) you have 8 hours to put more credit on.
it is incredibly well organised and rigourously policed so don't take a chance.