Spend the hundred… on a good rental machine. Many shops have a 3.5-4 gpm machine available. Rent an extra 50’ or 100’ pressure hose to make the job easier. I used a 2.5 gpm machine on exactly one job… it was excruciatingly slow.
Call Bob @ pressuretek and get everything you need to downstream with: elemonator, low pressure tips, and injector.
Then use the money you make off the jobs to get a decent machine. The 5.6@2500 pressure pro is a good unit. But you’ll want to set it up with a buffer tank.
I never got to use a surface cleaner very much with that machine (barely any flatwork in my area). But the consensus seems to be that it’s a bit on the low side for running an SC; adequate for residential concrete, but probably not commercial. Pre and post treating were highly recommended for good results.