While I'm a die-hard water-based pigment inkjet printers aficiando, I must admit they're not designed for fast, convenient and inexpensive double side printing.
Small format digital press with a decent RIP controller is an expansive toy, but - contrary to inkjet printers - it's born for such type of job. It accepts PDFs, makes automatic imposition (as option), prints on various kinds of inexpansive papers, and (with optional finisher) sorts, folds, punches, and creates booklets. It can print 40-60 A4/letter pages per minute, and the "click cost" is very low.