One point about these presumably "Eurorack" synths: they already have cabs and power. So, if you remove them from those and put them in a larger Eurorack case, you then have to factor the cost of how much of that larger case is being taken up by the device into the actual price of the K2, Model D, etc. And this can get spendy; let's take an example from the Tiptop Mantis here...
The Mantis retails for $335 (using US pricing here, same principle applies in any currency) and has 208 hp of space. This means that each hp has a cost of approximately $1.61.
Now, the Behringer Neutron requires 80 hp if you opt to put it into a larger Eurorack case. 80 x $1.61 = about $128.85. The "base" cost of the unit is $289.99 (looking at Sweetwater right now), so the total for a Euroracked Neutron actually comes in at $418.84. Also, you lose 80 hp of cab space for modules that don't have power or housing by doing this, which means that if you want that 80 hp of space after all, you'll have to spring for another Mantis. Now we're looking at $753.84, and this is starting to get ridiculous.
So, recabbing an already-cabbed synth like a Neutron, Mother32, etc is actually a big fiscal mistake. Don't do it! If you go with this "patchable" route (not a bad idea, really), this is a surefire way of overrunning your costs.