My normal recipe for getting a lot of money (In my experience, very cost effective, one gets a large output for less input)
Dirt Roads--400 fl. 1 turn
Ground Clearance--600 fl. 2 turns
Port--800 fl.(?) 2 Turns
Grain Exchange--600 fl. 2 turns
Those should get you going. Also, look for silver and gold provinces. Dub linh, Timbuktu, Arguin, Vienna, and a few more, those are very good. Base level mines are about 2000. The payout from a base level mine is about 240. It pays for itself within 9 turns and give you some profit.
A good approach is to think of things that way. How long until it pays for itself?