I think that if you settle for a layout that is, from the beginning, relatively mobile-friendly, responsive design will work perfectly and have minimal overhead.
The web is going mobile and that's something designers and developers have to learn to live with - don't think of your interface as a two-headed creature, but rather as a cross-device design which can adapt itself to different resolutions and screen sizes.
Responsive design won't make things easier if what you want to do anyway is two completely different sites. It will probably work better for you if you place the focus of your design at a spot that is slightly more mobile that desktop-oriented (in today's standards). Then it will be all about filling up empty space whenever it's available.
The web is going mobile and that's something designers and developers have to learn to live with - don't think of your interface as a two-headed creature, but rather as a cross-device design which can adapt itself to different resolutions and screen sizes.
Responsive design won't make things easier if what you want to do anyway is two completely different sites. It will probably work better for you if you place the focus of your design at a spot that is slightly more mobile that desktop-oriented (in today's standards). Then it will be all about filling up empty space whenever it's available.