Maya is pretty simple to learn. Much easier to learn than say 3dsmax.
Maya and 3ds however, will only accept lines and triangles. So if there is anything other than poly's or triangles you'll have to redraw it anyway. Just make sure you get rid of any n-gons floating around. .. or I could do it for you if the price is right
as far as Rhino goes.. MEH. If you want something cheap and can do amazing things..go with Blender. Rhino is still about $1000.. while blender is Free.
Maya Unlimited is about $3,500. Pricey but capable of amazing things. Plus since it's going to be using AutoCAD, if it were me I wouldn't mind spending the $$ in order to make sure things worked seamlessly together. Autodesk to Autodesk is much easier than say Autodesk to Cinema4d.