Commercial only requires 20hrs of training. Any time remaining to 150 can be done solo and in an r22, or a Cessna 172 for that matter. At your numbers that's a difference of $5200.
I was interested in the definition of a normal commercial course, I was expecting the response to be the minimum requirement, so I'll give you the same response that I would have given then.
If you're flying on a budget and plan to do as much soloing as you can, you're most likely denying yourself a whole bunch of very valuable training. Many students gain very little from a ton of soloing when doing commercial. Given everyone is different, and I'm generalizing, sure. Why not spend the extra money and get as much training you can get until you get to 150 total time?
In my experience, for many students, soloing is good for some things, but great for learning bad habits.
Why not minimize the time you're soloing? It gets lonely up there and your flight school is most likely going to restrict you from doing a whole bunch of stuff like emergency procedures, offsite work, long cross countries, flying in Bravo etc. anyway.
This is your opportunity to do all sorts of stuff e.g. spend as much time in Bravo airspace as you can; ask instructors to teach you what happens during a photo flight; go fly with different instructors, go fly as much night time as you can, you should learn something from every instructor.
Use the time constructively and maximize what you learn.
And we're back to it costing a tad more than $5k.
But it should be money well spent.