May need to get one and just wanted to know what the going rate is in Brussels.

Most cleaners are paid with "titres cheques" that will cost you 7.50 euro/ hour. You can purchase them from:

http://soeasy.sodexo.be

Just to add, if you are a Belgian ta payer, that €7.50 is reduced further (in your tax return, not directly) to something like €5.50 per hour.
Resist paying anyone to clean your house on a regular basis, except through titres-services. It's illegal to pay anyone cash in hand, if you don't want to use titres-services, then to legally do it will cost much more as you'll have to employ them directly and arrange social security payment and tax.
There are also one-off cleaners which you pay more for, such as for house exit cleaning which will present you for a bill like any other service, all should be legal.

7,50 is that all they get per hour?

Welcome to the real world Oscar, that's the minimum wage that many of us are on :-)

Actually, the government adds 14.22 euro to each "service check", thus the service company recieves 21.72 per hour. The employee themselves has an employment contract with a fixed income, as well as health insurance and accidence insurance.