You could always make one out of scrap metal like I did, I actually built two of them and although it was a few years ago now, I think that neither of them cost me more than $60 in material, one opens up to about 22cm and the larger one to 32cm. Off the top of my memory I think the larger one tops out at 60Kg plus,
It was a cheap way for me to get some large vises at a price that I could afford.