Lowest would be "Swill to the max", right?
1- make a PCB,
2- use
surface mount wherever possible. Solder the SMD parts.
3 - parts like switches must be soldered the old fashioned way (through hole). Try to get nice 'plated through holes'. Or maybe rivets, provided that they are not too thick. The through plating or the rivet will give a better bond to the board, so that we can.....
4- look at the underside of the PCB, see if legs -from the switches or other through hole components- stick out. Grind them off.
5- put an insulating layer under the keyboard.
I say you can either go...
1- normal (thin) PCB
5- silicone layer + stiff bottom, like aluminium, steel, carbon, nylon, wood, .....
or....
1b- thick, stiff PCB
5b- thin insulating layer. If one would grind, maybe even polish the underside, a rubber film would be enough
or possibly even....
1c- normal (thin) PCB
5c- thin stiff, insulating bottom. Epoxy/polyester, reinforced with glassfibre/kevlar/aramid. Maybe with a thin rubbery/silicone layer in between for evening out irregularities...
or....
1d- thin but stiff PCB. Somehow reinforced with Kevlar or Aramid....
5- thin insulating layer, just enough to prevent shorts & give the keyboard some grip on the desk...
All arm chair theory, I confess
So, would this be doable yes or no? Or am I crazy