When coming up with backgrounds for D&D characters, I sometimes see people cite “to gain treasure and riches” as their prime reason for adventuring.
For casters, this reason doesn’t really hold water. I mean, even a 1st level wizard can stay in a city and sell his services making ice with cantrips or offer other services, the value of which can easily match or surpass whatever they can get from a few kobolds wielding rusty daggers.
NPC casting costs in 3e was something like 10g x spell level x caster level. In 4e, spellcasters are even better off since at-will powers can be cast all day without rest. Can you imagine the potential industrial uses that Scorching Burst can have?
A fun(?) trick with D&D systems is to work out how to turn game mechanics and low level stuff into energy producing perpetual motion machines. It’s usually pretty easy.