A decent all-in-one doesn't necessarily have to be expensive. HP proves this with the Deskjet 3070A, an all-in-one that doesn't have extensive features but probably will be plenty for the average consumer. We tested it to find out what kind of all-in-one you get for £33.50.
There exist all-in-ones even cheaper than that, but then they are very limited in terms of features. If you want a model with a (wireless) network connection for example which is handy for today's mobile devices, you do need to spend a little bit.