Black and White film stock Vs Colour

[daveyboy]

hiya guys i just wonder what the advantages of shooting black and white film stock over colour is?
I know that it's cheaper but can anyone tell me what the prices for like a 100ft of colour and black and white s16mm stock is as i don't have a clue.
Also does it make the processing less expensive using black and white stock.
Thanks a lot
P.s. I've shot a bit of 16m and the picture was really grainy and there were marks on it when it was shown etc. I've watched Pi and Following and other recent Black and White films which don't have this. Is this just because they use better lenses? which are new and clean or is it something to do with the camera?

Thanks a lot
Dave