The easiest approach is binaural audio and headphones. There's plenty of premade stuff, as well as generators. Eg. iDoser.
A more serious vector is transcranial magnetic stimulation (TMS). That zany professor who always wears a baseball cap crooked (sorry, I'm bad with names) has some very promising results. You can DIY a "meditation helmet", as you put it, on the cheap & easy. Then just reasearch brain/mind states, and their corresponding wavefields and frequencies, and hook up some signal generators (a FLOSS option exists, by the name of siggen).
Do remember to keep a research journal, like a blog, detailing your efforts!