I started 'small' with my foray into dSLRs. I shot with film SLRs many years ago (before autofocus), and knew the 'lens before body' maxim. So, not knowing if this would be a passing phase or primarily for memory shots of the kids, or something that would be a passion, I got a gripped T1i/500D, 17-55/2.8 IS, and 85/1.8, 430EX II, and Manfrotto CF tripod/head - what I felt would be an ideal setup for family shooting while keeping to a reasonable (and spouse-approved) budget of $3K.
It turned out to be a passion.
Generally, my lens-buying pattern is that I research carefully and buy lenses to meet my needs. If it's something I'm positive I'll like, I buy new - that's most of my purchases. If I'm unsure that the lens is ideal for my needs, I buy used - for no more than 70% of the current new price, ensuring I can later sell the lens with minimal loss. I've got a good track record there. Of the lenses I have bought new, I've only sold two - the 85/1.8 I started with before knowing this would be a long-term endeavor (replaced with the 85L II), and the EF-S 10-22mm (after getting a 5DII and 16-35L II) - so, in both cases where I sold lenses I'd bought new, I chose the right focal length, but ended up with a better lens. In each case, I lost only $50 on the sale. To date, I've bought 6 used lenses - 200/2.8L II, 300/4L IS, 24-105/4L IS, 70-300 DO, MP-E 65, and 28-300L. Pretty good track record there, too - I've sold 4 of the 6; the 24-105 just to buy a new copy with the 5DII kit, the tele primes after getting the 70-200/2.8L IS II and 100-400, and the 70-300 DO because I wasn't thrilled with the IQ. For the lenses I sold, in many cases I actually made a profit, so in the net including the new lenses I sold, overall I'm a little in the black. The MP-E 65 I love. The 28-300 I just bought this week - intended as a travel lens, supplemented with a couple of fast primes - so the jury is still out. But that's why I bought it used, and for less than 2/3 of the cost of a new copy.
.