Layouts
Alex,
Your question is very broad. Perhaps you should start with the amount of available space you have. Next choice is to select a guage. In the overall expense of things, the track is probably the cheapest. I've probably spent $200 on track, and more than $1000 on rollingstock and loco's. Cost also depends on the number of turnouts. 25 yards of flextrack will cost you about $50. One doubleslip turnout will cost you $50. If you want to power the turnouts, then add another $15 each. etc etc. So as a handy guide, take the amount you want to spend, then double it, cause that's how much you will end up spending! Perhaps if you could give us some guidelines on the amount of space, whether you want some yards or not, how many trains you want to be able to run at once etc, we could give you some ideas on layouts and cost.
Hope this helps.