I just started and used the same logic. At $30 a day for rental, after three or four days I'm better off buying. Plus I'm gearoholic.
I still recommend you start by buying the boots. I got really lucky and found some 32 Lashed in my size that were almost new for less than $60. But you don't want to be cheap on the boots. Plus, if you need a size 12 or larger you may need a wide board.