Depends where you're going, but if you just book a flight and go backpacking in India/SE Asia/Australia etc you could stay in hostels - pretty cheap (also useful for meeting other people to hang out with). Also Lonely Planet list plenty of places in these areas that charge for a room not per person.
Voyages Jules Verne have a good selection of trips which don't attract a single supplement. Many of them involve travelling around and sharing tables for meals which can be nice if you don't like sitting in hotel dining rooms on your own. I travel on business quite a lot and I HATE doing that. Depends what kind of holiday you want really.