This article on Leslie simulators is really interesting. Make sure you to to the second page though, where he changes his mind completely (I really respect that.) The conclusion to the conclusion is that the Neo Instruments Ventilator actually sounds like a Leslie. They do cost $500.
Funny thing is you can get a Mahaffay Little Lanilei Rotary Speaker kit for only $400. That's basically an unpowered 10" rotary speaker (well, it's powered in that there's electricity going to the motor, but you need an amp to feed it.) The Little Laneli Rotary is probably the cheapest of the real-sounding Leslie emulators. It sounds real because it's actually a whirling speaker. It's only $399 but you have to put it together as a kit. And that involves some drilling and such, so you have to be at least semi-competent with wood.
What I don't really get about these is how the "brake" sound works on the stomp-box emulators. Because ultimately the sound of the Leslie starting and stopping is the most amusing part of it to me.
And I'm not actually in the market for a Leslie simulator, I'm just sort of vaguely interested. And it's not like I actually have any money lying around for such adventures.