Cost saving as has been said already will be neglibile either way. Some say single easier as it is slower. But some complex singles are faster than some twins.
The main difference is the PFL vs asymmetric circuits. I did mine in the single, and found a precise PFL took a bit of time to perfect. And when I tested I was worried about it. By comparison on my multi rating I found asymmetric stuff easy.
Another thing to consider may be that any extra hours you use, be it before test, or (hopefully not) after a partial will be much much cheaper in a single - usually more than half price.