Having a roti is awesome. Makes incredible chicken, and really does make any cut of meat juicier. Plus it's a lot of fun.
I lucked into a used Weber ring/motor for $20, and got the spit and forks aftermarket for a total of $30. So $50 overall, and I am very happy with that purchase. It does leak a lot of air, though-- mine tightens up pretty well with some folded foil pressed into the crack around half of the circumference. In a perfect world, I would have a CB, though I prefer a motor that can be plugged in.
Another option is to have a separate kettle dedicated for the rotis. Seal up the gap with foil or--better yet-- some oven door seal.