I built a small excel document to try to figure out roughly how you could convert money from the 2nd to 3rd.

The prices differ greatly with armor and some other equipment but here is the rough value conversion:

2nd 3rd

Brass: 4 = 1

Silver: 8 = 1

Gold: 40 = 1

Price multiplier: 2nd 3rd

Cheap armor 2 1

Expensive armor 1 2