Ljubljana is 2 hours flying time from London. Easyjet have regular flights from Stansted to Ljubljana with return fares starting at £40. Failing that you may want to consider flying Ryanair from Stansted to Trieste in Italy or to Graz or Klagenfurt in Austria and then catching a train to Ljubljana. There are no direct flights from Australia or New Zealand.
Train & Bus
Slovenia is easily accessible by train and bus from neighbouring countries and good rail links exist between Ljubljana and Belgrade, Budapest, Munich, Venice, Vienna and Zagreb. See Rail Europe for train info and Eurolines for bus info.
At roughly the same size of Wales, Slovenia is dead easy to get around. Slovene railways have an efficient, inexpensive service, with Ljubljana station acting as a main junction from where you can reach all corners of the country. See Slovene Railways.
Ditto the bus services. Ljubljana, Maribor and Koper all have major bus stations. You can generally buy a ticket on the bus but it’s best to book in advance if planning to travel to touristy destinations at peak season.
Driving is also highly recommended, but car rental is not particularly cheap. Slovenes use hitchhiking as a mode of transport, so there’s no reason why travellers shouldn’t do so — just so long as they exercise extreme caution at all times.