It's rather obvious your parents never collected anything worthwhile or got absorbed in a hobby for more than a little while.

You could defend yourself by stating that there are a lot worse things you could be spending money on....

It may not be an ideal solution, but I would suggest a PO Box.  My parents have since turned a blind eye on most of
my anime spending, but if the knew the amount that has left my account in the last month, their eyesight would improve
rapidly.  Having a PO Box has helped in that they never see the package arrive.  I don't know if USPS prices are the
same everywhere, but for a box that's about 4 VHS tapes high costs about $36 for 6mo. @ the local branch.

In my case it helped that I had "rented" the box to run registration for OhayoCon...