I dunno if it's a tip as such but I booked the cheapest flights I could find from Edinburgh (my closest airport) to cities reasonably close to Mostar and Olomouc while they were at their cheapest. I managed to get 6 flights for £120, but one is a 2 day flyer to Berlin and train both ways from there, and the other is 2 flights both ways to Sarayevo over 4 days, again with trains and 3 nights accommodation.
My thought process at the time was that by the time the 16th rolls around, the flights would probably have doubled but Im not sure if they have yet with it being wintertime. Have managed to get to all the European aways so far trying to do it on the cheap as much as possible. Got in the away end at Fredrikstad and Lublin, but could only get in the home end for Strasbourg and Shelbourne.