Find accommodation in Brussels

You don't have to hand over a cash deposit and NEVER do it before signing a contract. You can instead opt for a service from a bank where for a fee the bank guarantees the equivalent of a cash deposit. It's a maximum of 2 months rent which can requested as a deposit. If you go for cash deposit, you actually never hand over the money, you open a bank account in your name, with the details of landlord attached who must give their signature for withdrawal at the end of a contract.

A short term rent will have to be a fixed contract, so when you sign for 6 months for example, that's what you must pay, even if you then decide you wish to move out earlier.

Most universities/colleges have housing offices, where they'll have a list of accommodation specifically for students. Most students will have "kots", ie will have a room in a family house, will share a house full of students, the "kot" is simply a student room. Prices are often inclusive of bills and start at €300 a month and expect shared toilet/bathroom at that price.