You did well at that price. What is the serial number? That will help a lot with a date estimate.
Without the serial number, here is what I can tell you:
1. When the P-85 throw was introduced, it had 12 holes for the snares. The 2 hole model did not come out until 1973 or so.
2. The small knob tone control was generally replaced by the larger knob version in he tlate 1960s, but appears periodically on Acrolites throughout the 1970s, so that does not help.
3. The pointed corner badge started in late 1969, but was used through the early 1980s. It initially did not have trademark indicator but the later version had a "circle R" indicator above the "g" in Ludwig.
Rick