I definitely wouldn't recommend acrylic for most robot applications, but I did recently have the chance to work with both cast and extruded acrylic.
I found the cast acrylic to be closer in machinability and performance to polycarb and it is significantly cheaper.
A call to you local plastics supplier can offer lots of insight and alert you to materials that you may not know about.
My local supplier here in Michigan is
Total Plastics.