Which Commuting frame for 350?

I think I may have got confused with the difference between a 1.6kg road frameset for the money I didn't expect cyclocross frames to be 2kg+ for just the frame. is 250 a typo? I'm happy to spend more than that, I'd budgeted 350 but looking at frames I think i need to consider spending more.

how much would be a normal ratio?

Cyclo Cross frames do tend to be slightly heavier. However, do you think you will notice a 400g difference in frame weight. If you want a light single speed cross frame then Felt Breed, Kona Major One and the like are pretty light. I have owned both and they are both very nice handling, stiff frames. The Kona is the better of two and is superb to ride off road. The frame weight is around 1.5 kg and my total build is around 8.5kg. Most of the weight over a road bike is in the wheels and tyres and I could save around 1kg if changing to road wheels and tyres.
These are clearly modern Alu/Scandium frames that may not fit with what you are after.