I'm a big fan of the RPG maps, so I have figured out a few simple trigger setups.
1. The money sytem. Using gold is obvious. If you want quest related payments, then simple trigger a payment at the end of each side-quest. As far as purchasing, the simplest is to loop a set of triggers with a unit next to a building (ex: spearman next to a blacksmith). When you click on the spearman, he says you can buy an upgrade by clicking on the building. When you do, it deducts the amount by a tribute of gold, and then researches the purchased upgrage. You can also do a similar thing with hiring army units. In this case, simple have the trigger create the purchased unit next to the building, or off the screen, and task the unit to the player.
2. The leveling up system. There are a few different ways of doing this. There's the unique system. Triggers based on certain events or units killed, then trigger a specific upgrade, etc. Another system I like and am using in my current RPG, is based on the kill ratio. For every level, you set a trigger that waits for the kill ratio to equal a certain number (5 or something), when accomplished, you can research something, then start the next trigger that requires a ratio of 10, 15 or whatever.
For the upgrades, I'm letting the player choose between a swordsman or archer or mage. The swordsman and archer both have the most upgrades without switching heros, and the mage is going to be completely trigger based. Using a monk, and lots of trigger tricks.