I would have someone competent measure the depth of the worst pits and calculate the wall thickness that would remain after polishing them out, and go from there. Take the (hopefully knowledgeable) advice of said 'smith regarding it's safety margin after striking the barrels smooth.
Since it is a relatively low value gun you may want to consider striking the barrels and polishing/rust bluing them yourself to keep costs down. Since it's a beater/loaner I would even consider a top end cold blue application and resign myself to occasional touch up when it wears thin. I certainly wouldn't advocate this approach if it had any more value than a no-name trunk gun. JMO, others may disagree.
