Yes, it's terribly expensive and very hard to do, and none of you should attempt it; it will only end in disapointment, shame and failure.
Or...
Buy a 50mm 1.4/1.8 for non full frame cameras or an 85mm 1.2/1.4/1.8 for full frame as these work well in limited space. All telephoto lenses do it really well (See Jay Rocks stuff for details) but need space to work well.
Anywhere between wide open 1.4 or about f4 - will work really well, dilute to taste.
It's all about separation - the main background needs to be at least a few feet behind the subject. Works best on standing shots as on anything else it's hard to keep fanny* and face in focus.
When shooting you really want to shoot lots as the failure rate is higher than with regular in focus stuff. Target is either closest eye or hole of choice.
*That's an Imperial measure of fanny, IE pussy.