You can buy "distilled" water at many local supermarkets, at least here in the states. It has to say distilled on the bottle and can make no mention of minerals added, springwater, or anything that might indicate it has solutes in it.
While its certainly possible to make yoru own distiller, it would be massively more expensive to build than just buying an RO unit, not to mention rediculously expensive to operat eon a small scale.