I have successfully bent Plexi and PVC pipe on hot days by constructing a jig and, working in the direct sun, bending gently till the desired curvature is achieved. The problem with Plexi ('acrylic') is that it will 'sag' back a little, so you have to apply overkill at the beginning. I made a vent window for my van like this and that's what happened.
Ask a plastics shop and see what they'll charge; it might be worth it to avoid such hassles. I would just dread the cost of 1/2" Plexi or (worse) Lexan.