Is there a way to get infinite gold in Majesty 2: Monster Kingdom?

No infinite gold but...

According to this Majesty 2 thread in Steam, you can gain gold each time you cast a Kingdom spell (i.e. Magic Lighting or Healing spells).

You just have to open resource.pak file as it was a rar file, extract spells.xml into /resource.mod/gameData/magic (create /magic folder if needed). Then modify via Notepad. As simple as that.

I post the relevant part of the thread:

Open Resource.pak, extract the 2 files that are in gameData\magic (spells.xml and spell.xsd) into x:\Steam\steamapps\common\majesty 2/resource.mod/gameData/magic

Take into special consideration gamedata\magic\spells.xml open up with notepad and change the cost of any spell to a negative number and you gain gold whenever you cast a spell. e.g. spell name="magic_lightning" cost_money="-2500" icon="magic_lightning" player_spell_gfx="thunderbolt" target_gfx="thunderbolt_posteffect"

This will grant me 2500 gold for each click.

Good luck!

Easiest 'spell' to use is the rogue's Extortion because it can be used so early and quite cheaply. In the spells.xml file just search for magic_extortion and change the money_cost to -2000 (or however much you want each time you use Extortion.