Actually, it shouldn't be all that hard to set up a small or midsize sailboat with advanced automatic sailcontrols without having to shell out a gazillion dollars.
Instead of gazing up at fully automated superyachts, for which Jim Clark's "Hyperion" remains the prototypical example (he was rumored to be able to sail Hyperion from behind his desk at home) one only has to study modern, radio-controlled model yachts (typically built at scales around 1:10) to find all or most of the electronic control components. The AMYA (American Model Yacht Association) organizes dozens of races each year, such as the East Coast 12 meter (really 60 inch) class fleet
(shown rounding a buoy here).
Such highly controllable model yachts typically cost around US$ 2,500 to 5,000 including one or more $ 250 "smart winches".
For years now, some model yacht enthusiasts have even been working on building yachts that would be capable of crossing oceans. I believe there is even a big prize for the first model yacht that manages to cross the Atlantic (or has it already happened perhaps?
None of this answers the important question why one might want to do something like that of course. However, technically (and financially) building a highly automated 20-30 ft sailing vessel should be well within the reach of quite a few sailors.
Have fun,
Flying Dutchman