Surely the engine wouldn't need frequent rebuilds if it is essentially a bike motor swapped in. IIRC the standard motor in the original radical was a stock hayabusa motor, which is pretty reliable and cheap if you blow it up.
The trans shouldn't need to be rebuilt either unless it's a sequential. I think they make both H pattern and sequential versions, the sequentials all need rebuilds but I'd be shocked if it was sooner than 100 hours.
I don't have personal experience with the radical but I'd venture a guess that it would be cheaper to run that your RS and would be way cheaper if an incident occurred.