I am afraid that there is many more commercial grade RAT on the market as we think, that are unknown to us, and some of them are below 1000 eur range. In wikileaks published emails of Hacker-team one can fell magnitude od such RAT development.
Here is overview of recent target attack with customized RAT
http://www.welivesecurity.com/wp-content/uploads/2016/05/Operation-Groundbait.pdf
Anatomy of targetet attack on specific jurnalist
Hacking Team and the Targeting of Ethiopian Journalists
Since best samples of these threats are polimorphic (even on the fly), we must forget to any signature based "antivirus" and "anti-malware" solution.
Until now i was sure locked down computer with "default deny everything" policy of Comodo would help me here, but after last confirmed fileless memory vectors of attack and process injects/kidnapp i am lost .... so waiting to cruelsis results on this one.
There is no signature to these RAT, every customer gets customized-freesh sample, if target sre big enough even custom CC url. And combinated all that facts with valid signature .... its really hard to think on any defense.