the things you need to look at is cost of every day running:
Electricity (I can say that I left it printing for 12hours) and altough it went up, it wasn't by much. maybe a few pence in my day to day electricity costs.
PLA - I use PLA, its around £20 for Kilo (300m approx). Once you pass the initial setting up phase and you have run your test prints etc. you don't really waste anything.
Files - there are enough free files out there that you don't really need to buy anything, unless you want top of the range prints.
Printer - I had a cheap one to start with. I then bought a better quality one and you can tell the difference (on the Dads Thread, the failed Pigsty was done on the cheap Chinese printer, the rest was done on my new one).