The Paragon Silver Clay kilns could be used for this purpose. I keep
mine hot all day for pennies. This series features a one-piece
ceramic fiber muffle with the coils embedded, and heats so quickly
you might not even need to keep one at temp - mine goes from 70 to
1500 (Fahrenheit) in about 15 minutes. They include a digital
controller for precise temperature control, and are great for
annealing, enameling and glass fusing in addition to silver clay.
Because the elements are embedded in the walls of the kiln, the
walls themselves glow red hot. Metal and glass should not be allowed
to touch the kiln walls or bottom. Do NOT coat the inside with kiln
wash - it voids the warranty. Instead, line the bottom and 1/2" up
the sides with some 1/8" ceramic fiber paper to protect the kiln
against inadvertent spillage of enamel, molten metal, etc.
Most of the Paragon Silver Clay kilns sell in the $750 US range.
Here’s a link:
If you want something cheaper (in the $400 US range), other
manufacturers of small glass annealing kilns make versions without
digital controllers. They provide a temperature readout dial and you
control them manually with a rheostat knob same as your cooking
Most are made of fire brick and will be slower to heat, but cost
around the same to run. Others are metal cases like toolboxes or
mailboxes lined with ceramic fiber. These heat and cool quickly but
most have a useful upper temperature range of about 1000 Fahrenheit,
due to the thin walls.