The basic meaning of treulio is "to use up", so it can mean "spend (time)", "wear out (clothes)", "digest (food)".
If you want to say "spend (money)" you use gwario.
Treuliais i noson o dan y sêr (I spent a night under the stars)
Gwariais i £100 ar docyn trên (I spend £100 on a train ticket)
Incidentally, in south Wales you can use hala (spend, send) for both colloquially.
Halais i noson o dan y sêr
Halais i £100 ar docyn trên