Boy that sucks, but glad to hear that you can continue your journey. Thanks for the writeup, always interesting to read about how stuff like this works out.

Never have your bike overstayed...

a few years ago i did it for one day... my temporal importation was ending on a sunday and went on tuesday to renew it...bad idea

Basically the girl from the desk told me that normally bike is blocked by customs, some tribunal procedures can follow as it is considered as fellony...
Fortunatly for me she told me to go to a medic, made him made a certificate i was ill, went to the big biulding on 9 de julio to have the signature of the medic certified and came back after having all these papers.
In case you had an accident in Argentina and was sent back to your country i guess you could have used the paperwork related.

With all the COVID thing i guess it is going to be less strict... but at the same time Argentina s government need money...

There is always a way when you know the correct persons (but i don t so i can t help you with such things).
The 50%+30% are in fact around the same thing i paid making the offical import (the 30 are 21%VAT + some others things) based on a value referenced in what is called the blue book of customs. You can however "fight" this based price if you can show what is the actual value of the bike in your country of origin. (to which you ll have to had costs of certified translation).

PS Value will be set in pesos at national bank rate, Western Union uses another rate wich is nearly twice the official one (1u$ = 85 pesos officially, western union makes it at around 1u$=150)

ANother reason why a carnet is a good option - they have to stamp you out so you have proof. I realise that this doesn't help OP, but it may help future travellers.