Drive trains will last almost forever if you keep them clean and lubed. I replaced my Dura-Ace chain at around 4,500 miles and it was still well within the 50% limit, I'm guessing it could have gone another 4,500. I'm a bigger rider pushing 200 lbs with gear. Cassette should last several chains.

I go through a couple bottles of lube a year ($20)
New shifter cables about every year ($20)
Chain every 4000 - 6000 miles ($40)
Brake cables can go longer ~ 2 years ($20)
Brake pads get 2+ years ($30)
Tires, not quite a year (I run 2 rear for 1 front so 3 tires = $120)
Cassette, every couple years ($150)
Bar tape (2 x year, it doesn't wear out, I just like to change colors = $25)
Chainrings, mine still look good.

I ride around 4,000+ miles a year, and keep the bike as clean as possible and well lubed.