I use a product called mini-cutoff saw available from the tool outlets like Harbor Freight and Northern Tool. It has a 2" steel blade with a thin kerf, a little vise to stabilize the tube, and slices right through carbon arrows. Also like that that the steel blade will not shatter like the composite ones can.
But it will only handle up to about 1/2" dia. tubing. Looked for a small cutoff saw with a blade around 3", but no luck yet. The arrow saws, available from Cabela's and the archery outlets, only handle arrow size shafts, and you have to push the shaft into the blade, rather than stabillize it in a vise and lower the blade over it as with a cut-off saw.
If your straight shafts are under 1/2 inch, the mini cutoff might work well. They are under $50, including a supply of replacement blades.
Should also mention that I use a small buffing wheel to buff the ends of the shafts after cutting.