Hi Bill. First of all you should check out Mel the Terrain Tutor.
http://www.theterraintutor.co.uk/
He has a vast collection of excellent YouTube videos that tell you how to build sorts of things including hills, roads, rivers, trees and hedges. He focuses very much on building from scratch so the only cost is the raw materials.
For ECW, if you have some buildings already then I would go for hedged enclosures next. (Could be walled enclosures in North England or Scotland. A duck pond for the village could also be a nice touch.
Some woods would also look nice. Commercial trees are available at a range of costs and the videos above include how to make them yourself.
Your armies also need a camp so this can add some nice features. Tents, wagons, camp followers and assorted baggage. Renedra do nice tents. Warlord have some lovely wagons, and of course do ecw civilians for camp followers. Ainsty Castings do nice baggage such as assorted barrels and boxes etc.
Hope this helps?
.
