Decade voltage divider switching
Vacuum relays tend to be high power and expensive but mercury wetted reed relays are not expensive.  $5 2A 1kV

https://m.ebay.ca/itm/GI-Clare-Mercury-Wetted-Relay-type-CUP-P001A505-1-form-A-one-NO-2A-1000V-coil-5V/253552671880?hash=item3b08eabc88%3Ag%3APfcAAOSwY45UOw2G&amp;_sop=15&amp;_sacat=0&amp;_nkw=mercury+wetted+relay&amp;_from=R40&amp;rt=nc