It depends where you live. A taxi from my apartment to the airport is about 145RMB and takes about 45 minutes. Subway plus maglev takes 60 minutes, and costs less than 50RMB (maglev is 40RMB if you have a subway card).
True. I'm happy to pay 40 RMB to avoid standing up for half an hour (and getting home half an hour earlier), but not the extra 100 RMB on top to save another 15 minutes (and contribute to global warming) :)