My son needed speech therapy. He had an 'adorable' lisp and couldn't pronounce "R"s correctly - in the parents eyes only though.
He received help in a public school, in the 4th grade. It was almost too late to correct it. But he worked exceptionally hard and his diligence paid off and he no longer has any issues.
He had been enrolled in a private Christian school where there were no services and they did not watch for such issues. I am forever grateful that we left that school, and transferred to a public school, where teachers are trained to observe and make recommendations.
My hunch is that you will pay out of pocket for this service, when you can wait a few months and he can take group and individual speech therapy lessons in a public school. Having peers around for my son was critical for his success, as they motivated each other to do better. He really enjoyed the social time with his group of speech therapy buds.
Again, personally, I recommend you wait, read lots, talk and discuss everything that pops up and ask the teacher for guidance come the fall. But don't ask the first day, give the KG teacher a couple of weeks to get to know everyone, then bring it up and ask her to observe and start the process.
4 is young and there is plenty of time to catch up. GL!