Over the past couple of years or so I have purchased several 4 letter names in various tlds, all an acronym of our company name, the values were roughly:
.asia - $250
.co.uk/co.in/in/eu/mobi/tel/us - regular price
.net is currently available for $1,100.00
.com is unused and the owner simply does not respond to anything!
They're 2 letters, 2 letters as in "aabb" and actually noticeably spell a very well known English noun but with one extra letter. I don't know if that makes sense, just think of "off" and "ooff"!
Therefore I would say that $10-15k would have to be very reasonable for a recognisable name and to put it into perspective I sold an 8 letter noun for $160,000.00 a few months ago...so, do you want ten of those? :-)