I went to a glass shop in college to get some frame glass for a weird sized frame. The frame shop was going to charge an arm and a leg. The glass guy ended up being very busy and short handed that day. He handed me a cork backed metal ruler a glass cutter, a pair of leather gloves and showed me what to do. I cut my glass and helped him out a little with other cuts so I did not have to pay for the glass I was getting. It really was that easy. I left with a glass cutter and some advice- Buy a good quality glass cutter and Don't be afraid to cut the glass.
When you go get your glass cut ask to watch then do it your self from then on. You will save money. Oh yeah get a sanding block too to polish the edges.