That's interesting. I wish that were in the DMG. Now that I look back at the "running a business" rules, it occurs to me that they waste a ton of space on a mostly-useless table of results, that they could have instead used to list examples of the size/cost/profit of businesses of various sizes. For example,
[table="align: left"]
[tr][td]
Business[/td][td]Staff[/td][td]Startup Cost[/td][td]Monthly Profit[/td][td]Suggested Ability Check[/td][/tr]
[tr][td]
Inn (small)[/td][td]1-3[/td][td]30 gp[/td][td]4 gp (±8 gp)[/td][td]Charisma (Persuasion)[/td][/tr]
[tr][td]
Inn (large)[/td][td]4-6[/td][td]75 gp[/td][td]10 gp (±10 gp)[/td][td]Charisma (Persuasion)[/td][/tr]
[tr][td]
Mine (small)[/td][td]1-5[/td][td]20 gp[/td][td]5 gp (±10 gp)[/td][td]Intelligence (mason's tools)[/td][/tr]
[tr][td]
Mine (medium)[/td][td]6-25[/td][td]100 gp[/td][td]25 gp (±25 gp)[/td][td]Intelligence (mason's tools)[/td][/tr]
[tr][td]
Mine (large)[/td][td]26-100[/td][td]400 gp[/td][td]100 gp (±50 gp)[/td][td]Intelligence (mason's tools)[/td][/tr]
[tr][td]
Shop (common goods)[/td][td]1-2[/td][td]50 gp[/td][td]10 gp (±5 gp)[/td][td]Charisma (Persuasion)[/td][/tr]
[tr][td]
Shop (uncommon goods)[/td][td]2-4[/td][td]250 gp[/td][td]10 gp (±25 gp)[/td][td]Intelligence (History)[/td][/tr]
[tr][td]
Shop (rare goods)[/td][td]3-6[/td][td]1000 gp[/td][td]10 gp (±100 gp)[/td][td]Intelligence (Arcana)[/td][/tr]
[tr][td]
Tavern[/td][td]2-5[/td][td]20 gp[/td][td]2 gp (± 2gp)[/td][td]Wisdom (brewer's tools)[/td][/tr]
[/table]
Startup Cost. You must pay this once, to get your business up and running. It covers the cost of initial equipment purchases, any legal licensing required, and recruiting your initial staff. However, it does NOT cover the cost of any real estate required, such a building to serve as a storefront or mineral-rich land in which to mine.
Monthly Profit. Each month, your business pays out profit equal to the gold piece amount listed. This assumes that your staff is running the business, in a sensible, low-risk manner.
Ability Check.If you yourself take a hand in running the business, spending at least 15 downtime days during a the month, make an ability check (suggested checks are listed for each business). On a 9 or less, subtract the parenthetical modifier from that month's profits. On a 10-19, add the parenthetical modifier to that month's profits, and on a 20+, add twice parenthetical modifier to that month's profits.
The numbers in the table are SWAGs; this is just an example of how I would prefer business-related rules to work.