I think a better tact would be to simply look at the worlds basic Cost of Living expenses, correlate them with your own experiences (i.e. grab a generic salary survey of the web -- heck, even Parade Magezine has an annual sorta-salary survey), and then go from that.
I mean, if "most people" pay "30%" for housing and food, that can give you a base line to work from, and then go from there. How much do YOU pay for housing for example?
For example, while our current U.S. house-for-sale market is going berzerk, the rental market is quite stable, so that gives a good idea of what what basic shelter runs for each month in different areas.
While it's true that the market reflects its customers, i.e. expensive areas have people that make a lot of money (duh), and prices adjust accordingly, it can be easier to find references to costs for housing and other basics of life. And the best part, even if you just pull those numbers out of the blue sky, once you index everything else off of them everything is balanced.
Simply put, you're just making the local market "work". You can't rent apartments for $2000/month if there aren't folks willing to pay it. If folks are willing to pay it, how much would they need to earn each month to live there? Once you know that, you can then set things like meal prices, car prices, etc. So it all evens out.
Obviously you can make exceptions, government policies for example, rent control, coporate housing, etc. But, even then, you adjust the incomes appropriately. It's clear that if the corporation is paying for the housing for you, they're not paying YOU for housing -- you don't need it, so you can reduce pay accordingly.
With a little spreadsheet and calculator magic, you can come up with numbers that "seem legit".
Once you have the numbers, you can then work out any exchange rate details in interplanetary cash is an issue, or you need to covert local Cubits to Imperial Credits.
Anecdote: I remember back in the day about some guys hearing that they could earn, like $40-50K/year working in Japan (this was in the 80's), and they were all eager and excited by that number. But at the same time, they weren't considering the cost of living etc. that goes with it, so $40K/year over there may well not be the same as $40K/year over here.
Anyway, my 2 cents for ways to derive some of your own numbers from a few base factors and some fiddling with a pencil.