hmmm,..there's a lot of power tools you can use,...so far the cheapest is to use a dremel tool,.....and to get the rough edges off,..you'd have to sand the edges to smoothen it up.
theres a tool called "nibbler" thats really nice to use with window mods. it lets you cut all kinds of shapes....even outline a figure with very smooth results...the electric ones costs around 750USD tho...so the best way is to use a dremel.