The first thing to note in case you don't know is that barristers do not have salaries. Nearly all barristers are self employed, which means that they are not paid a set amount per year, and instead bill and get paid for the individual pieces of work that they do. The reason why this is relevant for the answer to this question is just so you appreciate that even individual barristers will earn different amounts every year, and sometimes those incomes can vary quite significantly year to year depending on the cases that you do. You may already know that and understand the difference, but I thought it was worth clarifying in case you don't.
With all of that said, yes, incomes vary significantly as a barrister in any area of practice. It depends on a whole host of things including how good you are as a barrister, how good you are at cultivating relationships with solicitors and clients, how good your Chambers is, how good your clerks are, and just how lucky you get. But a commercial practice is one of the more lucrative areas you can work in as a barrister. The top end commercial sets in London will often be the sets that people discuss when talking about a commercial practice. At those sets you can and probably would earn really significant sums of money very quickly. As in over £100,000 within a year or two at most, with your earnings increasing pretty significantly from there. A friend of mine is at one of those sets and recently became a KC in his 30s. I wouldn't be surprised if he's earning seven figures at this point, in fact I suspect he probably is.
However, you have to understand that those sets are the exception. Only a very small percentage of barristers practice at them in the context of the Bar as a whole, and both the practices that those barristers have and the money they earn is the exception in this profession. It's not something that you should expect to be able to achieve. It doesn't stop you aiming for pupillage at one of those sets, but it shouldn't be understated just how competitive it is, and in the round how unlikely it is that you'll be successful. There are a lot of very good barristers who would never realistically have been able to get pupillage at one of those sets.
But that's not to say that a commercial practice isn't still a route to earning a good living, because it is. Even at smaller London or regional sets, particularly in the likes of Birmingham, Manchester and Leeds, but even in other cities like Liverpool, Bristol and Newcastle, a commercial practice at a decent set could still see you earning six figures pretty quickly (within a few years at most) and settling at around the £200k to £400k level once your practice is established. That is a wide range, but the bottom line is that ultimately you can make a very comfortable living as a commercial barristers at any decent set.
Just one final point to note. You may have asked about a commercial practice because you're aware that it's one of the highest earning areas. When it comes to financial stability as a barrister, there are plenty of other practice areas where you can earn a good amount of money to the extent that you're financially very comfortable. Even in some of the 'lower' earning areas, such as crime and family, you can still make a perfectly good living (and earn £100k+) in the right situation. So it depends how you are comparing these earnings to other roles, and what is the determining factor for you. I wouldn't recommend that you become a barrister for the money anyway, because frankly there are other careers and industries where you can earn more. But if it is because you are attracted to being a barrister, there are other practice areas that you might be better suited to beyond commercial where you can still make a very good living. You have plenty of time to research those, though.