Watch out with laser cutting and aluminium: Some grades (like 7075) have copper in them, which reflects part of the laser beam. This can (and in the copper fractions in 7075, likely will) lead to damage of the laser!
Some other substances will also reduce the quality of the cut.
Instead, I would consider using water jet cutting: There's no heat build-up and as such less distortion and better retention of material properties near your cutting edges (especially for strain hardened or heat treated grades), you're not restricted in material composition (like you are with a laser), accuracy and edge finish are fine for a chassis plate and as far as my knowledge goes, for small batches and one-off work the costs are very similar.