For as often as coolant is changed (rather infrequently these days), I wouldn't use any other than the OEM coolant, even purchased for a high price at a dealer. The difference of $10/gallon today is small over the course of 3-5 years and tens of thousands of miles.
If I owned an older car that truly took the "old green" coolant, I'd find some coolant that's specifically the "old green" coolant, likely a house label like Advance or Peak. I don't think Prestone sells the old formula anymore.