According to namebio, ypa (dot net) sold for 1,555 last year. ypa (dot net) 1,555 USD 2016-02-16 GoDaddy
Value of a .net acronyms dropped this year and its not easy to tell whether the value of LLL.net will increase or decrease in the future.
For now, approximately I would say: mid XXX to a reseller and low XXXX to an end user.
Three letter .net domains have stayed within the same price range during the last decade. To resellers they are typical going at mid $xxx - low $xxxx. A quick search shows a few potential end users for this one.