B&W only tends to be cheaper if you do it yourself. Around here B&W is no cheaper if done commerically and can be more expensive.
Personally I'm a B&W person. I see B&W better. With colour I tend towards snapshots.
From the sound of it you're looking at about the same cash outlay either way. So why not pickup a few rolls of each and give them a try?
B&W film is going to be cheaper then most [all??] slide film. If cost is the only issue then go B&W. If you are more a colour person go colour and shoot less if need be.