You can save a little bit by going for Vintage DT880/600's from the 1980's (Look for them particularly on ebay.de) - should be less than 1/3 the price of current models - also the Revox 3100 and Revox Synergy (Rebranded beyer DT880/600 pro and standard respectively). If you read through the threads on headfi - you will find comparisons of the 80's DT880 to the current models - and the 80's versions are frequently preferred. (you may want to read the Vintage Beyer thread)
There are also other top HP's from the 80's that are worth a listen and can be purchased for reasonable $$$ (mostly pro studio monitoring headphones!) - such as AKG K240, K340, (best found on ebay.de - make sure you get the 600ohm models, bargains can be had for the K240, K340 are still a bargain given their performance, but starting to be a collectors item) also Koss Pro4x (best found on ebay.com). The Koss is almost completely forgotten nowadays and I remember it as being competitive with the DT880's when I worked in audio in the mid 80's. (I have a set being delivered this week I hope! - then I will post a review)
I am happy with my M-Stage, and if I was focused on a working system (not wanting to tweak and mess about) - I would order it with the Class A OPA627 mod (with the resistors mounted directly to the OPA627 adapter) - if you want to experiment, order the class A socket, and the OPA627 adapter seperately.
With the OPA627-ClassA you are effectively getting a Lehmann Black Cube Linear (almost identical circuit) with an upgrade.
Alternative is also the LovelyCube (this is more of a complete Lehmann Black Cube Linear copy) - this one is more suited if you are into more intense DIY - some of the DIY'ers claim it sounds better than the M-Stage - Others have heard them both and said they sounded the same.
I Have the Firestone Cute Curve (which is class AB not Class B as the websites say), I compared it stock to the M-Stage, it was very close but I felt the M-Stage was better. (I had the Cute Curve running with an OBH2 Creek power supply - so upgrade from standard, and the M-Stage running stock OPA2132)
I have since tested the Cute Curve with the Class A upgrade mod (same as M-Stage) - and with various opamps, all I can say is that it works and sounds good - beyond that requires extended listening, and I am still doing extended listening tests with the M-Stage - the Cute Curve will get its turn later.
Cute Curve comes standard with OPA2604 - I fitted the 2604 to my M-Stage and compared over several hours to OPA627 / HA3-2525 - the other two opamps sounded better than the 2604 (all were running in class A mode) - and I think I preferred the OPA627 (Jury is still out on the final decision).
Once I have finished with the testing and bedded down the M-Stage (couple of months), I am going to go through the same optimisation process for the Cute Curve. - The Cute Curve is intended for my desk, and the M-Stage for my lounge room.
Good luck on your search