OK, than in your position, where you will mainly be travelling between few set locations, and not bringing it into train for work or clients to show, the SFF solution that VUK suggested is actually a really good alternative.
SFF can be anything from 10 Liters to massive 40 Liters, it has no defining measurements, just that it should be "smaller" :- ). There are some super thin cases that can fit E-ATX boards, and super pretty big that can barely fit ITX. A lot of options, a lot of research to do.
There is whole Reddit section dedicated to this community where you can look for inspiration, as well as lot of youtube videos, particularly from OptimumTech.
https://www.reddit.com/r/sffpc/https://www.youtube.com/channel/UCRYOj4DmyxhBVrdvbsUwmAARegarding airflow, there are generally two ways these PCs are built:
1) With air-tower which usually has to be pretty small for most cases with few exceptions. This is incredibly bad idea for 3950X, yes people do it but just because they can, doesn't mean it should be done. The CPU can be run in "eco" mode which is under-volted by stock bios in that case. For what is worth, my 3950X runs hot with massive NH-D15 in super ventilated case, people want to tell me it's "ok" to run it with tiny pancake cooler :- ) ?
2) With AIO cooler, but then the radiator has to be positioned in top of the case otherwise the amount of heat will wreck everything, esp. the PSU which always positioned like Puzzle piece and when overheated will start spinning fan into ridiculously loud DBs (like 40).
So my advice, is to go smaller, but not too smaller. Something like Cerberus with handles
http://www.sliger.com/products/cases/cerberus/ would be great with 280mm radiator or Lian Li TU150, also with handles that can accomodate NH-D15 or NH-U12A.
The "sandwich" cases (because the GPU is sandwiched with riser cable into vertical position) are much sexier...but with shit airflow.
People will generally say that it works, but that is not such a clear-cut case. Everything in air-constricted case will deteroriate. ITX boards have already very limited amount of VRM capacity in terms of both power stages and heatsink volume, X570 boards have chipset fans that are blocked by GPU even in their full-scale ATX formats, but in ITX or mATX the effect is compounded. Board where both chipset and VRM will run at 100C year-around will eventually deteroriate and you don't want to put expensive board into trash after a year.
Regarding price, they aren't more expensive by default. The cases are quite often more 200 Euros than 100 because they're usually aluminium for weight (and because almost all of them are manufactured in LianLi factory).
Otherwise all the rest costs the same.
