I have an expensive pH soil tester. Used it a few times years ago and was kind of a waste of money. You can watch your pH with a water tester. Know what it is going in, check runoff to see what it is coming out and you should have a pretty good idea what you have. And over time, you may not even use the water pH pen much. You eventually learn to be consistent and watch the plants and I've gone through whole very successful grows without using a pH meter one time.
I have found out if you watch it early it prevents problems and the young seedlings do better though. I generally just spot check runoff these days...if you use the same water and nutes all the time, there just aren't many pH problems you can get. Don't forget to flush on schedule and you're usually pretty good to go. My last grow I let pots get too acidic late in flower only because I didn't flush on time. Final flush was 2 weeks away so I let them go. Bad move, they probably didn't uptake the last couple feedings and buds didn't swell the last couple weeks like the other grows. Sometimes one gets too confident, live and learn. I do a lot more spot checking now, just in case.