I have full elite troops and a town with elite garrison. I also have 5 million denars in my wallet.
The trick to making easy money is to develop your smithing skills. At the beginning of a game, add to your endurance and smithing skills at every opportunity, until they max out. Prioritise your smithing skills over your fighting skills.
Learn forge weapons that you can sell for tons of denars. Typically, you want to forge and sell double-handed swords, polearms or javelins. The raw materials you use for forging is way cheaper than the denars you get for selling the finished product. Just having the weapons in your inventory is like having denars in the bank.
For example, I have 8+1+1 crafted javelins in my inventory. Each javelin is worth 16000 denars. That is a value of 160,000 if I decide to sell them. The reason I haven't sold them is that sometimes the traders in town run out of money. So I would have to move to another town to cash them in.