Travelling cheaply is a matter of making the right choices for your budget. it is not difficult to overshoot your travel budget; one wrong choice and you can spend much more than you originally intended to!
There are a number of creative solutions today such as couch-surfing, which can practically cut down your costs of accommodation to zero. The idea behind couch-surfing is that you join an online community of people open to the idea of having people from different cultures to stay on their couch and perhaps doing the same.
For those who would rather not stay at anyone's house, there are always accommodation choices that can work out to be cheaper than hotels. Guesthouses and hostels, particularly youth hostels are often very affordable, even in big cities such as London. Holiday apartments such as Amsterdam holiday apartments can work out to be a good option for groups or for long-term visitors.
One of the best ways to plan a cheap holiday is to book in advance. Travel fares, including airline fares as well as local transportation can be significantly cheaper when booked in advance. Also, it's a good idea to watch out for deals that are often happening online.