Does the WM16 work-area/table suit your CNC requirement?, do you use it rarely as a manual mill? Is the spindle suited to the work that you're looking to do? If the answer to any of these is no, then look elsewhere (but you'll struggle on your budget).

I converted a SX2.7 (It's a Trigger's Broom - so little left of the original now I refuse to call it a Sieg) having got bored of spinning little wheels by hand - they can be made into reasonable bench mills with little effort. Besides, the conversion can be fun. But you'll be on the edge of your budget. Manual wheels?, you'll suffer the commutating forces of a stepper, you can get by with a MPG / electronics. To be honest, other than the quill control (which I retained) I don't miss the manual wheels at all.

The 3040 might polish a bit of steel, but probably not much else.