I used Contiki once many years when I still was well within the targeted age group, eg 18-35. They had various price points depending on the type of accommodation you choose, ranging from campsites to budget hotels. It's cheap for various reasons I think. One, entry fees to places of interests, optional activities etc are excluded. Two, price is for land package only, so not inclusive of airfare. Three, they seem to own n operate some of these budget accommodation. Four, they have volume, and so benefit from economies of scale. The good thing is the people in the tour group are all in the 18-35 age group, so no kids or old people to slow down the group. This is from my experience donkey years ago, so not sure if things have changed since.
But my advice is, if you are traveling in the off peak season, eg like fall/winter period, consider building your own free n easy itinerary. Quite easy to drive around. Alternatively, the train network is quite good generally in continental Europe, between England n France (Eurostar) n within France itself. It's a great way to experience the place. I used to just hunt around for accommodation every time I reached a new city or town. Or if you want to play safe book in advance, now easy to do through Internet with travel sites like trip advisor. Last time before the age of internet I had to go to each local tourist information office, get the info n make phone calls or ask the customer service to help make the reservations.
For a traditional travel agent with great prices and experience in digging out all sorts of alternative routing solutions try Muhibbah at Beach Rd
Many travel agents focus only on the most obvious solutions getting clients from Point A to Point B Eg SQ, TG, Cathay, Emirates, ANA and when these flights are full many will have no idea what to do next especially during peak seasons
Muhibbah saved my back-side more than a few times by thinking out of the box with weird connections when the obvious connections were full (during X'mas Eve, New Year's Eve, Easter and Thanksgiving holidays etc etc)..... sure there was the trouble of transits and time wasted connecting to other flight(s) .... but it still got me there and back in the end
Then book a local land tour with the right itinerary