Star Ruler 2 is on sale for $12.49 on steam. http://store.steampowered.com/app/282590
It has a very unusual diplomacy system; personally I find it better than the usual but some people dislike it. In addition, the economy revolves around setting up planet sized supply chains and lacks a "galactic bank", which I find makes large games much easier to manage. However, some people dislike the change. It still has some problems but the dev are doing a pretty good job fixing them. Unfortunately, the game hasn't gotten much exposure and the dev are probably going to run out of money in about a year. They'll continue updating the game until their money runs out and they'll probably make an expansion but a sequel, or second expansion, is unlikely.