I have been trying to get to the Association for Internet Researcher's annual conference for a few years now. These past four years I have priced plane tickets and two years ago, actually made hostel reservations in Sweden and registered before asking for a refund unable to afford the trip. This year I even tried fund raising with crowd sourcing and raised 25 dollars for the trip. I can't really justify spending our household budget on this trip.
I did spend household money on a SAS programming conference this past spring. This was directly related to my work and career so this was justified as there were threats of layoffs this spring at work. So this was an investment in my job.