Look at the price for size of 00 models now it's not that bad. An average 00 gauge 12ton van is now around £20-25 in 0 it's around £40-45 RTR a good kit is slightly less. As for track it depends on your abilities and time you have spare. But in all honesty there are not huge savings in costs. By the time you add hours spent and tooling you break even unless you need something super accurate RTR track is a perfect way to start. Look at the likes of Hattons, Rails or Sheffield and Tower models for your bargain track. Is almost always heavily discounted and often 10-20% below list price.
What era are you into Simon? Oh and welcome to the world of 0 gauge. The only thing you will miss is the availability of certain stock but that is changing month by month with new announced things to come.