Yanmar tillers used to be cheap because the dealers received more than they could sell - one with every Yanmar imported because the tiller had been on that tractor since new and the salvage yards really needed to move them out.
Times have changed, Japanese tillers are seldom imported, and anyone buying one now is paying a price competitive with a US tiller.
I paid $200 for the most faded RS1400 on the lot. With a full set of genuine replacement tines. It works fine. Deals like this don't exist any more and in fact that importer is no longer in business.
$650 today is still a fair price, not excessive.