|Fighter Level||Weekly Expenses|
This is based on the midpoint between the experience needed for the current level and the experience needed for the next level, divided by 100. Every time you go on an adventure and return successfully, you add 1 to your weekly expenses: when your expenses meet the amount listed for the next level, you gain a level. Thus, your level is based on your perceived wealth + your perceived adventurousness.
This approach does leave the door open for "cheating" (spending more than needed to trick people into thinking you are more successful than you really are.) This would work something like carousing rules, with a reaction roll every time you spend money equal to the expenses for the next level; on a Good result, your current expenses go up by 1. Spending double on one party/project gets a +2 increase, triple gets a +3, and so on. There would, of course, be drawbacks for a Bad or Very Bad reaction, and bonus effects for a Very Good reaction, but I haven't decided on those just yet. If you brag about monsters slain on your last expedition, for every monster of equal or higher level slain, you earn a +1 bonus to expenses if the reaction roll is a success.
It's something I want to think about some more, but I think it has potential.