Grout? in Another Open Diary refugee

When we moved in John said 'I like the dark grout, it doesn't show the dirt...' Guess what? After two weeks in the place I just realised that it's not 'dark grout' - it's FILTHY! It's actually cream grout the same colour as the tiles, only it's got years of dirt ground into it and my mopping the floor didn't do anything but loosen it a little so that the dirt was more visible (instead of being uniformly black, now it's patchy in spots, and it's screamingly obvious to me that it's in fact filthy dirty grout.) Now what do I do??????? Anybody know how much professional grout cleaning costs? I can just imagine how many centuries of scrubbing it would take to clean it myself. :( (looked up a service online and it's 42c a square foot, which doesn't sound like much until you do the maths. 42c x 1200 square feet of tile is $500 of so! Guess I'll just have to learn to live with the filth...