Depends on how "clean and accurate" you need. For reasonably clean and accurate, I would make a pattern that looks like the part from some MDF or whatever falls to hand. Then rough out the lexan as close a you can to the final shape with a bandsaw, jigsaw, table saw or method of your choosing. I would then fasten the pattern to the rough part with double sided tape and cut the final profile on a router table with a trim bit with the bearing following the pattern. By removing most of the material in the roughing step, the router bit is less likely to gum up because the chips have a place to go. If there are any inside corners, make sure your router bit is small enough to get in there. You're not going to cut a 1/8" radius inside corner with a 1/4" radius cutter. If it's all outside corners, the size of the bit doesn't matter too much. If you've not done this before, try a couple of test cuts just to see what happens. The feed speed matters(slow to give the chips time to clear) as does the router speed (probably slower that MAX). A bit of paraffin wax (candle) on the bit will help the chips to not stick. WD 40 will work too, but it will compromise the double sided tape fairly quickly. I have cut lexan shapes using this method and it works for me. It may not work for you. For less clean and accurate, rough it out and cut to the line with a belt sander depending on what the part looks like. Again, inside corners are a pain so a rotary sanding drum on a Dremel would probably work. Remember, I don't have a clue what your part looks like so all the above may be inappropriate.
