Any suggestions on inexpensive headphones for a Nakamichi SoundSpace 5?

I believe the headphone output impedence is 40 ohm.  I use this system for late, in bed, listening which is why  the Nak system.  With my main system I do not listen to headphones, hence the interest in something for the bedroom system.  Thanks for you thoughts/experience.
What do you consider inexpensive?Can you use open back or do you need closed back for sound control?Output impedance is pretty low,300ohm cans like Sennheisers might sound slow & muddy.My go to reference under $500.00 is the HiFiMan HE400i(about $200.00).Absolutely superb cans,easily competing with $1250.00 Audeze LCD-2F’s(which I also own)..They also come in closed back but I have no on ear experience with any closed cans to comment..
Hi freediver,  thanks for the input and what you suggest are the very ones I was thinking of from HiFiMan.  Even though I have had much in very, very good audio gear ..I have not had any headphones since from  Audio Technica Eletret Condenser and Stax models around 30+ years ago. 

I am fairly focused on what I listen to, mainly classic acoustic Jazz and female vocals that lean towards the Jazz and Standards family of music.  I do not have a concern for open back designs where I will do most of my listening.  My main system is in a room where I am free to listen, but in my bedroom I am mainly interested in more casual.....heading off to sleep listening.  In my main system I have had tube and solid state components and my speakers for many years have been from Magnepan, Martin Logan and back when I started it was the original large Advent and Dahlquist DQ-10.  My favorite piece of amplification/pre-amplification ever is the original Conrad Johnson ART pre. ..just to give you an idea of what my choices have been.  Take care and Happy Holidays to you and your loved ones. 

My favorite headphones for bedtime listening are my Massdrop Sennheiser HD6XX. $200. Super comfortable, great sound.