What would you normally charge per sqft? I'm not a long time veteran doing tile but I'd be considering the size of the tile since smaller tile = more grout lines to scrub - and smooth or rough tile which creates dirt catching spots that have to be scrubbed out. Also the 20% of stuff you are moving, are you talking a quick move or major work?
It does really go back to what Mike said....how long are you thinking the job will take? 8 hours at .50 nets you $2000 @ $250 an hour. Not bad at all. Probably going to take you longer, you think?