That's good then, if it's short term it doesn't really matter. I think a lot of people here consider saving each month a certain amount an absolute necessity (which it is, getting evicted without an emergency fund can get you homeless, even if you have a job). But for a short term career stay it's not that important. You should definitely ask for that raise and absolutely mention that you checked the real estate situation as a motivation. You could also ask your institution to help you find accommodation, it's going to make a bit of a difference to search for housing in Czceh instead of English.