is it at reasonable to pursue the attacker by contacting the
Most likely not. Any moderately skilled attacker would simply steal someone else's wifi or use a proxy. You can then contact that proxy's ISP which is probably located somewhere in Togo and you will never get a reply. If the attacker sets up servers for backdoors and alike, they will be either temporarily or also hosted abroad.
Is there a damage/cost threshold that would make pursuit worthwhile?
Yes but that threshold is really high. Even when the damage is staggering, pursuing someone over the internet is neither really effective nor is there any hope to get for example stolen assets back. One big reason why cybercrime is so profit-yielding is the fact that it's hard to track down the attackers.
If the source of the attack is from another country (Russia, China), you have absolutely no chance to catch the attacker. Of course, the same applies many other countries.
Is there a relatively standard or productive manner in which companies
(or individuals) deal with attacks on a legal level?
Yes, at least in Germany. This is highly depending on the respective national framework of course. Here, critical infrastructures have a central office to report cyber crimes to and get external help, but pursuing the attacker is usually beyond the scope of the investigation. Companies even have to report certain attacks to the police.
As a private individual however, you will most likely only be able to complain to the police. And the police is completely incompetent in that regard.
Almost all methods against cybercriminals are mitigation and prevention, since tracking someone down who attacked from abroad is borderline impossible.