Earlier quoted context omitted.
"Dexcom has a CGM system that hooks up to your phone/watch, but is only available with prescription (and is extremely expensive without coverage)" Can you elaborate ? What do you mean by extremely expensive ?
Prescription is required: http://www.dexcom.com/faq/do-i-need-prescription-obtain-dexc... My "extremely expensive" was unfair. Some quick searching suggests ~$650 for the transmitter ~$100/week for sensors. "Not cheap" would be more accurate.
Don't let the fact that lifesaving treatments are often even more unaffordable shift your frame of reference.