The only belt drive talked about in that thread is the C3 unit, which is $900.
He's asking about the parts to convert the 11/12 into a 13, which is what I'd be looking for if I had an 11 or 12. There's no way the parts would cost $900 to convert it.
The C3 is nice, but it's pricey, I'd bet with stock stuff you're looking at 300-500 MAX & you're then running stock parts so replacement is cheaper & easier.
That thread seems like it started talking about this, but someone must have looked at a 13 & figured out which parts would need to change by now?