SeemeCNC is a high quality operation and you will get a good version of the rostock from them. You can get faster print speeds with a delta due to the different movement system and smaller end effector mass. the biggest con with delta is that you're pretty much limited to Bowden tube extrusion and the limitations of that system with control of how much filament extrudes. With a cartesian printer it's slower but potentially capable of higher quality due to the ability to use gear drive extrusion. If you're going with a prusa design cartesian printer (bed moves in Y axis) then makerfarm is the best bang for the buck. The build volumes are different size/shape between the two types. If youre going for an xy cartesian (bed moves in Z axis), I would honestly get a makerbot rip like a Wanhao duplicator or flashforge. These are nice if you're lookng at enclosing/ adding heat to the build volume.

If you do go delta take a look at openbeam usa. I like their kossel kit design very much and I think it's close to your range.