Aachen has many good and affordable hostels and hotels.

Most affordable ho(s)tels
Both of these places are about 25 minutes away from the congress center by bus:

• Hotel Buschhausen, from €22 per night in a 3-bed room, see here.
• Youth Hostel Aachen, from € 23,70 per night (for a bed in a dormitory), see here.

Find a good hotel deal close to the center
Through these online booking service you can find yourself a good hotel just a little more expensive but much closer to the congress center:

• Aachen City Page
• Booking.com

For example in Hotel Ibis Aachen Normaluhr a two person room costs only €55 per night.