hy qwerty in this case, considering that your machine is allready "4th axis ready", you should go along with your initial vendor, or, pehaps, a different vendor of the same brand.I would like the rotary to have full contouring capabilities too
however, if machine is still under warranty, then you may lose the warranty if another fanuc vendor is messing with it
even if initial price is high, at least it is a guarantee that it will work, but, even if you have the money 2 go with your initial vendor, be sure that your controller + 4th axis will deliver real 4th axis motion, and not only positioning : not all controllers are capable of delivering 4th axis interpolation
other options :
... there is a kitagawa stand-aloner, thus a 4th axis with integrated nc ( Quinte ), that requires minimal stuff to be conected to a cnc, and had been desgined as portable, like to move it between different cnc brands; contact kitagawa, but considering the versatility of this products, it may be more expensive
... try to buy not a new one from your initial machine vendor, but an original refreshed one, if available; some rotary axis producers also bring to back to life some of their used products
... if you are lucky :
...... maybe there is someone that has a 4th axis on the shelf, and wished to get rid of it
...... get a random 4th axis from somewhere, and find someone that can conect it with your machine
kindly