I had decided on getting my own snow-board boots after the last, very painful, experience with rentals. Went to Jimbocho with Rainer and found some really good and reasonably priced boots. They seem a little tight, but they are supposed to reshape to fit your feet after a while.
After I got those, I just had to get better bindings since the rentals I got were quite worn-out and you end up keeping everyone waiting while tightening them. And, since it would waste so much time to have the rental place put on the new bindings on the rented board, I thought might as well get my own board, which off course, needs its own carrying bag and grips.
Total cost: You dont want to know. All I can say is that its the most expensive sport Ive done. Wait till I start sky-diving.