Hey - I'm even cheaper than that! I've just found a piece of foam which is darkish grey and non-shiny and makes colours look perfect. I'll still buy a Lastolite at some point, but the foam makes a great cushion for the bottom of the camera bag when not in use!
You do not need true Lastolite, just buy chinese stuff. I have one and it is ok. Useful if you'll have mixed lighting and set WB at certain place, for example.
If I'm ever unsure I still use a grey card and spot light meter. (Got to make myself one of those "Black Hole" boxes to really test if my new bellows-style lens hoods are really keeping out most of that stray light). http://www.imatest.com/docs/veilingglare.html
Cool - I've seen those dark box things in the middle of studio camera line-up charts, and had forgotten about them. Thanks for the interesting link; I've found even my makeshift grey reference is very useful - as Vitaliy says, particularly in mixed lighting. I've only ever used white balance using white paper before, but the grey makes more sense.