Uh, a new Bell 407 is north of $4 million and that's before it's equipped for medical flights. You aren't buying one of these for $500k used, at least not one that's air worthy. Eurocopter EC135 are a bit cheaper, but not by much.
-> https://www.globalair.com/aircraft-for-sale/helicopters
-> https://www.globalair.com/aircraft-for-sale/helicopters