These sockets can be made for $3 each or less if you have some non-working tube equipment that you can scavage the sockets from. Even bought new the sockets should be $2 or so. Add to that a few machine bolts and nuts, a piece of wood for a base and a few feet of hookup wire and you have all you need.
Parts needed for each socket.
(1) 6.5" of 1x4 pine or poplar works well
(1) 8-32 x 1.25 machine screw
(3) 8-32 nut
(3) washers to fit the machine screws
(1) tube socket of the correct type
(2) 1"x .25 tube for socket support
(2) 1.5" wood screws that fit the socket mounting holes
(4) adhesive rubber feet
hookup wire (get some 600 volt insulation wire)
I picked up a box of 100 each of the machine screws, nuts and washers because they were cheaper that way.