Easiest way I make platinum with the least amount of effort is in Misty killing the wall guards. The guards along the wall are all mid 30s in level with the exception of Deputy Budo. Every guard, with the exception of Deputy Budo, will always carry a generic spear that sells for rougly 9-10pp each and a shield that sells for 1-2pp each. Killing all 6 guards (again not including Budo) will land you 72pp at a vendor(with decent cha) and 1-2 pp each in corpse cash. My 50 monk drops every one of these deputies in just a few seconds. I am not exactly sure on the spawn rate in Misty but I am guessing its 20ish minutes maybe with the exception of the two guards at the gate, Deputy Keld and Deputy Asler who spawn much more quickly.
This will of course ruin your faction with the Rivervale Merchants, the halfling mayor, Guardians of the Vale (the halfling guards) and the Storm Guard (Im guesing these are the dwarven guards in Butcher). I have absolutely ruined these factions and to this day the only problem I have had with it is that it is somewhat annoying to enter Rivervale and walk around with guards attacking me. ;)
There might be easier ways but I do not know of them. This is by far the easiest way I have found to get pp in a short amount of time by myself. Just be wary of Budo, who can be a handful sometimes and does not always drop a spear and the gate which can be messy if you are kos and can not yet handle the 2-3 dep fight.