If you go on Expedia click multiflights either Continental or United will do it. Reasonable is well (about £370 each)
I am thinking about it myself but not sure about Royal Caribbean ??
I have booked out on thomas cook day before and back on zoom. All in £570 and that includes premium economy on zoom. thomas cook were fine when i last used them (lots of space and on time!). Royal Caribbean I found were very good and would recommend. Not been on Radiance before but made sure I booked an aft balcony for the views. Paula.