Recommendations for headphones under $400?

@freediver 
They are definitely well within budget!
Quick eBay search shows $210 new and $150 preowned.
Research time......

uberwaltz,

     freediver has a good suggestion with the HiFiman He400i's.  Very nice planar magnetic headphones.  
    If you want to go with a planar magnetic, there are also some from Monoprice that are less expensive headphones that are very similar to and may even be made by HiFiman.  They look very similar and are $200 new, here's a video review of the Monoprice M560's:
www.youtube.com/watch?v=vgAf-_aGR5M&list=PLsm0YcQ-5gn0jpVfKNZuimVUB7OmbLpEy&index=14
     This site, Zreviews on You Tube has a lot of headphone reviews, including the He400i's, Oppo PM-3's, Sony Z7 and many others. Freedriver is spot on; the bass is very good but doesn't go really deep.  These really shine in the mid-range and treble, though.
 
     Probably a good site for your search.  Please post back on what you decide.
   Thanks,
     Tim

uberwaltz,

There are also some good headphone deals on Massdrop, here’s the link:

www.massdrop.com

Massdrop works with many very good headphone manufacturers to offer ’special Massdrop versions’ of their headphones at bargain prices contingent on Massdrop acquiring a predetermined minimum number of customer orders. Once met, the manufacturer builds the headphones and the orders are fulfilled.
These headphones are assigned a unique Massdrop model number but are typically very similar in performance level, promo model# and looks to one of their regular models. It’s not difficult to identify which specific regular model they’re basing the promotional Massdrop model on.

The reality is you’ll get a very good headphone at a bargain price,

Tim

I would agree with noble100.  I've bought several headphones from Massdrop over the years.  IMO, I think the best deal (price/performance) on the headphone market is the Massdrop Sennheiser  HD6XX, which is the exactly the same model as the Sennheiser HD650.  You'll need a decent headphone amp to properly drive these headphones, but once broken in, they are an excellent value.  I'm not sure what model you have, but my Grado GH1 w/ G Cups were very comfortable and the bass was very good.  You may also want to look up the Grado line, especially if like their sound signature.  Good Luck!

I did buy a pair of the hifiman h400i and am awaiting delivery
Hopefully this will do the job!