Earlier quoted context omitted.
Very interesting. The connection to French is not immediately obvious as both "purchase" and "buy" would translate to "achat". However, "por chase" in French is "for the chase/hunt" which begins to resemble some definition of "purchase".
In which French did you find "por chase”? (this is not aggressive, I am french and this does not mean anything but it may be a dialect or some as ancient French?)
> From Middle English purchasen, from Anglo-Norman purchacer (“seek to obtain”) from pur- (from Latin pro-) + chac(i)er (“to chase, pursue”). Compare Old French porchacier (“to follow, to chase”), which has given French pourchasser (“to chase without relent”).