These units are not commonly available for sale in good working order, and are quite expensive in any condition.
Typical costs based on 2006 research for prices paid for this kind of equipment:
One advantage of this set is that the 350 watt 4CX350F PA tubes can be substituted with the slightly lesser 250 watt 4X150D and 4CX250F types which also have the 26.5V heater voltage. They will do just fine of you don't abuse the unit and are rated for 590 watts of output under normal conditions anyway. Since the PA tubes are 26.5V heater voltage, they are less called-for and therefore not very expensive.
The greatest caveat in operating the unit is to tune it properly, by the book. When properly tuned according to the two tuning knobs and two tuning meters on the front panel, you will always get the correct match and the 400W PEP output (Remember, this was designed to be tuned up by soldiers, so it is purposely ruggedly made and simple to operate). You can get almost 600W PEP/CW out of it by using a scope and "loading it up", but this is a mistake because the screen current in the PA tubes will be excessive and can cause the tube(s) to fail. If this happens, the HV power supplies will just shut down, no other harm done. These sets are tough!