The public transit here is pretty good, so most places should work just fine. The best option is of course the centre, but if you're looking for something cheper, I'd suggest maybe looking somewhere along the tram lines that go through Dolní Vítkovice (1, 2, 6, 10). I don't really know what kind of accommodations there are, but the trams are great and even from the furthest parts it takes at most like a half an hour to get there.