This could be a major restriction to your backpacking trip, however if you have a proper plan and careful considerations are put into it, you should be able to make most of it out of your budget.

Budget usually determined the duration of your trip, mode of transport, places to stay (accommodations usually makeup the largest portion of your expenses) or even your meals. Spend sometime on this, determine how much you can spend on your trip, and revise on the number of destination to visit or things to do (usually lesser, urgh !!!).

When travelling, always asked for discount whether you are getting a bus tickets or getting an accommodation. By showing your student pass, you might get away with cheaper rate. This is especially true when travelling in Europe and North America, many businesses are offering discount just to get student to use their services.