Hmmm. I don't know, so this isn't based on experience, but I'd be very suprised if [the average person] could do 0 -fATPL in < 1 year modular. I know some people can, but for the average person I think that's a VERY tall order.
Full time, I reckon 15 months is a sensible plan. Unless you plan on just learning the answers - which I'd suggest is a VERY dangerous practice -from Bristol (or similar QB) the exams alone you will need 6 months for. PPL 3 weeks (for C 50 hours) + hour building (another 6 weeks if we pro rata the PPL out) + five months for professional training (taken from potkettleblacks post) + 2 weeks MCC (plus another 2 weeks if you go JOC also - I think it's useful, lots of people don't).
All this adds up to about 14 months, absolutely flat out, no breaks. About the same time as an integrated course. Would consider yourself very lucky (and talented!) if you can complete 0 - fATPL in less than that time.
costs....Don't know, but again most of the mod guys I've met have said that it's not strictly true that you can save 40% on integrated and the differential is much lower. That said, it IS undoubtedly cheaper.
good luck