I just bought:

The used 20gal long tank I mentioned.
A bag of cypress mulch (I can always get Aspen instead and use the mulch for gardening if I go for the kingsnake).
A 10-20 gal UTH (the 20-30 looked too big to me).
150 watt lamp for heat bulbs or CHEs.
75 watt incandescent bulb.
A half log hide.
A big water bowl (big enough for either snake to soak in, and it'd help raise humidity for a BP).

I still need:
A thermostat for the UTH.
A dimmer for the light if I use it.
Various supplies for cleaning the cage.

Anything I'm missing (besides the snake )?