I would approach this by trying to convert the income rate generated by the core material into a per-day rate based on level.
http://www.enworld.org/forum/showthread.php?402507-Deconstructing-5e-Typical-Wealth-by-Level
The guy who started that conversation used the treasure charts to create an approximate WBL chart. That's a useful shortcut, so we don't need to do it ourselves.
http://simul16.tumblr.com/post/131004985629
This guy draws out how to calculate how long, in days, it takes to gain levels based on xp demand and assumed reward from the adventuring day. Really peels back the engine's cover.
Based on the assumed xp output of the adventuring day, you can create the encounters that would provide that xp and the matching monetary rewards. Divide the total by the number of required days spent gaining each level, and you have an income rate, and how that rate changes as the characters gain levels.
It is somewhat subject to your campaign and how you structure encounters and pace them with downtime. I have taken the information from those articles, assuming they are correct, (which they seem to be) and calculated it out.
1=140-0=140÷1= 140g/d
2=280-140=140÷1= 140g/d
3=420-280=140÷1.5= 93.33g/d
4=560-420=140÷1.5= 93.33g/d
5=4500-560=3940÷2= 1970g/d
6=8400-4500=3900÷2= 1950g/d
7=12,300-8400=3900÷2= 1950g/d
8=16,200-12300=3900÷2= 1950g/d
9=20,100-16200=3900÷2= 1950g/d
10=24,100-20100=4000÷2= 2000g/d
11=42,400-24100=18300÷1.5= 12200g/d
12=60,700-42400=18300÷1.5= 12200g/d
13=79,000-60700=18300÷1.5= 12200g/d
14=97,300-79000=18300÷1.5= 12200g/d
15=116,000-97300=18700÷1.5= 12466.66g/d
16=134,000-116000=18000÷1.5= 12000g/d
17=362,000-134000=228000÷1= 228000g/d
18=590,000-362000=228000÷1= 228000g/d
19=818,000-590000=228000÷1= 228000g/d
The downside to this system is that you cannot calculate income this way for a level 20 character, because there is no level gain point to base it off of.
There's a weird pay rate dip at levels 3 and 4, because it takes longer to gain levels there, but there is no corresponding pay rate increase. This is an artifact created by the fact that we're having our pay rate emulate income by advancement. I don't see why it would hurt to just keep using 140g/d through to tier 2. A similar dip happens between levels 5 and 6, and 15 and 16, which are caused by the switch from one random treasure chart to another. Again, I would recommend replacing that dip with the rate from the previous level.
Also, rather than basing the pay-rate on the adventurers' level, it should be based on the expected difficulty of the adventurer. A lazy adventurer who only takes easy jobs shouldn't make the same kind of money as one taking very difficult jobs.
Assume an adventurer (or party) of an appropriate level, a reasonable amount of spellcasting, a reasonable length of time, and calculate a payout before starting.
– tzxAzrael Jul 12 '16 at 22:16