If you want to be rich then become a doctor. They tend to get better starting salaries than anyone else simply because they are super high in demand. However, you have to be really passionate about medicine and saving lives rather than just care about the cash, considering the rounds of interviews and examinations to get the degree in the first place and then study for a very long time before becoming a qualified doctor. This is probably what drives money hungry people to commerce rather than medicine lol thank god somewhat for that. I wouldn't want to entrust my health to a doctor who is nothing but greedy lol
In my opinion, commerce is the most overrated degree ever. At least half my peers are doing commerce degrees and for the majority it's the same attitude with the "I wanna be rich" thing. Unfortunately, many people I know who have interests in other areas (and not commerce) decide to do commerce only because of this "rich" stereotype when they should at least be doing combined commerce degrees.
If you intend to do a commerce degree only, you have to do WELL in it to stand out from the millions who've done the same degree...and lets face it, the finance/accounting industry for example is too crowded and competitive these days plus they are NOT in high demand compared to other fields like education or medicine.
So really only the cream of the crop manage to get into those big firms with a good starting salary and can work their way up the corporate ladder from there. The rest generally end up doing mediocre jobs for a longer period of time and find it much harder to climb the corporate ladder unless they successfully start their own business or something of the like; either way getting rich becomes much more difficult.
Combined degrees are more common these days and the reason for that is that you acquire more diverse skills in different areas making you more desirable for employment. It also makes you stand out a bit from the pile of commerce only people. Furthermore, it allows you to explore any passion that is NOT in commerce.
So basically, if you're really into commerce and always do well in it with a passion then go for the single degree. However, if you have other areas of interests such as science, engineering, arts or law but still want to do commerce (but you're not that passionate about it) then you're better off doing a double degree.