It is quite difficult to make end user appraisals because end user sales not necessarily will follow the general market trends as reseller sales tend to do. It depends very much on the end user in question. If it's a large company it will not make much of a difference if you ask for 1 or 5K, but a small business owner might simply not be capable of paying more than 1K. Overall you should be able to get low - mid $x.xxx from an end user. Three letter .net domains are valuable but are not easily sold. Be proactive and contact potential end users.