A half Detolf housing a robo about 2 inches in length would be roughly equivalent to a 6 inch Syrian in a square meter cage
So while it may not seem as nice as having the full Detolf,it is still a very good amount of space for a robo and if necessary could be expanded to a full Detolf over time.
For a sand bath,try and put it on a platform that can double as roof cover.This is good for confidence,and with new hamsters especially dwarf hamsters the more roof cover the better.You can put all sorts of things on platforms,and as long as they're made properly for whatever species will use them they're very good to allow more free digging and hiding space but also prevent a lot of things from getting buried!