I intended to take the train to Budapest from Venice and maybe stopover in Vienna for one night but after researching how long the journey will take may look at flying.
Well, if you do decide to fly, just remember that most of the low-cost airlines (including WizzAir & RyanAir) have rather tricky pricing systems. It might sound a bit illogical, but sometimes buying your flight ticket too early is almost as expensive as buying it too late. From our experience, too early is usually >3 month in advance, while to late is <1 month in advance. It's not a universal rule or anything, but just from our experience cheapest tickets for low-cost flights usually available during period <3 month & >1 month
I then thought the sleeper train may be an option but we are a party of 5 - travelling with my parents and two sons and haven't been able to find info on a couchette for 5 and wonder how comfortable it will be.
Direct overnight train from Venice to Vienna has couchette compartment for 4 & 6 passengers (prices start from 59 & 49 euro per passenger) and sleepers (triple, double & single, from 69, 89 & 129 euro respectively). So you basically have a choice - buy 6 berth compartment (maybe even all 6 berth, so it would be all to your family) or purchase a combination (like 3 berth in 3 bed sleeper compartment & two in double sleeper). 6 berth couchette compartment are OK in this case, will look something like
this Also looking for advice on prices as haven't been able to get prices of tickets as its so far in advance to try and work out whether inter rail pass will be more cost effective.
That's a usual question regarding pass vs. point-to-point tickets. We here a bit bias here on
europetrainsguide.com, since in most cases would advise to go with point-to-point tickets (mainly because in 90% of cases it's simply cheaper). But in order to give you are rough estimate let's count:
London-Paris-Geneva: tickets for
EuroStar train London-Paris can be bought for as low as 39 GBP (or 48 EUR), while for high-speed TGV train from Paris to Geneva from 25 EUR. Obviously both tickets are discounted & require purchase far in advance
Geneva-Zermatt: again best case scenario is discounted SuperSaver tickets from 37,2 CHF (or 30 euro)
Zermatt-Brig-Milan: Zermatt to Brig with SBB SuperSaver tickets is 14,8 CHF & another 23 CHF for discounted international ticket Brig-Milan
Milan-Venice: here again bought in advance discounted ticket (offer 'Super Economy'), price can be as low as 9 euro per passenger
Venice-Vienna: as we already mentioned above, couchettes can be bought from 49 euro, sleepers from 69 euro, seats from 29 euro)
Vienna-Budapest: discounted international tickets start from 19 euro per person
As result, if to sum up everything it will be roughly 200 euro (with 6 berth couchette on Venice-Vienna leg) with point-to-point tickets for the whole trip London-Paris-Geneva-Zermatt-Milan-Venice-Vienna-Budapest. Obviously price can be cut down even more, but then it will require certain changes, like going to Budapest not by overnight option or not via Austria (but via Slovenia) etc.