The best way to get to Bansko (cheapest) is to get a taxi from Sofia airport to the bus station "Avtogara Ovcha Kupel" the regular bus takes 2 1/2 hours from there This does not cost agreat deal (13 leva per person - single). See times at http://bansko.org

You can go on the train, I have not tried this but I have been told it is not the best expeience in the world.

Car hire, good idea.

I have found quite good prices for a resort bus to Bansko at www.resorthoppa.com but have not used this service myself.

You can get a mini-bus to pick you up, but this is expensive as they have to come from Bansko, drive to Sofia and then take you back and you have to pay for both journeys!