You can buy new bottle cutters online (here's a good roundup of options) but their ability to cut different sizes, angles, and bottle shapes are severely limited.
Of course, there are loads of potential projects to be had, so instead of buying a bottle cutting jig, let's make one!
Instructable-y Sbanas (who, by the way, is only sixteen years old and already bit by the DIY bug) came up with this easy solution using scrap wood and a sheet glass cutter you can get at any hardware store. Some cuts, some hardware, and boom! - a fully adjustable cutter to start slicing up bottles in no time.
If you want to make one. the only recommendation I'd make here is to perhaps increase the size. This guy works well for 12-16 oz soda bottles, but if you're interested in using larger wine or liquor bottles, a longer length and wider platform will do you well.
Check out the step-by-step tutorial here: Adjustable Glass Bottle Cutter