You have a great plan. If he really wants rehab, he will call them. If he just wants to hit you up for money by saying what you want to hear, you'll find that out too.
Meth is some bad stuff. My daughter used it.
I totally 100% completely etc. agree with Echo on her brilliant idea not to give him an answer tonight, if in fact he still insists he wants a rehab. Make no promises about anything until you have "down" time to think it over and talk.
Hugs and good luck! Tell us later on how it went 