Original price unknown
The Yamaha CSDX is the prototype of the DX family, which would later be released as the Yamaha DX1.
This was probably built between the GS1/GS2 line (1981) and the presentation at NAMM in 1983. Only one image likely exist of this prototype, featured on an unknown German brochure and on Jean-Paul Verpeaux's "Technique complète des synthétiseurs", a book published in 1985. It already features everything that will later be found in the DX family: 6 operators, algorithms, keyboard scaling, fully digital inputs and LCD data display. The case is still mostly made of wood, but the number of switches and controls is comparable to the ones on the final unit.
It's worth noting that the logo shown on this prototype has the same typeface that would be adopted by Yamaha after 1986/1987, not the one used on the DX7 and not the older style of the CS family.
In October 1983 the final DX1 was already taking shape, as seen on a review on Electronics & Music Maker. This last prototype only differs from the production model in the printing of the top panel, showing a scheme of a single operator instead of the list of algorithms.