I could be wrong, sorry if I am, but I don't understand why you would want a sub $100 case when you're going to do a custom cooling setup. Yea this case looks nice, but <$100 sends up flags in my mind with respect to build quality and materials. A custom loop will set you back a good $300 right? So you might as well get a really good case to go along with it. Never done a custom loop before though, just my thoughts really.
Don't be sorry but I do think you are wrong in your views here. Just because it does not cost over $100 does not make it cheaply built, it smartly built. Think about this, without any drive bays to machine and fit into it the cost of producing comes way down. NZXT did not go this route, they still have 3.5" bays and optional mounting for the 2.5" drives, FD brilliantly (IMHO) used existing space and material to mount 5 drives. This cut way back on cost making it. Perhaps they are able to pass that innovative design savings on to us and did, good for them.
All of FD cases are top notch quality, have never read a review of any of them that said the quality of build was lacking in any way, just read 3 reviews of this case and they all said it was excellent quality and also not one single "Con". Looking inside of this case, well there is just not much in it, very little material went into the interior construction, yet it can accommodate everything needed in a high performance rig with a ton of WCing capability, I think they have a winner here
The H440 is a much nicer looking case I think, if you want something really pretty then the H440 it it for sure. Without the 5.25" bays I think it's the best looking case on the market for any price, just my taste of course. But for a simpler case than can do even more than the H440 can this Define S is going to be hard to beat.