i have the Fairtex Maddox grappling dummy (version 2 with hands and feet) and while it was pricey, I think it was worth it, at least for me. I use it all the time to do drills. There are a few positions you cannot train (for example de la riva, x-guard) but otherwise great for closed guard, side control, half-guard, etc.
It does not of course replace a live person, but that is not what I wanted it for. I need to break down and slowly go over moves, exploring the positions at my leisure so I can remember them. Has helped me tremendously as cannot drill as much or as slowly at the gym
And it is decent for more realistic speeds to integrate the component parts into a whole. It weights 60lbs (majority in the legs), and I am going to buy a weighted vest to make it heavier and more balanced weight-wise.