They are trying to do as much as they possibly can to make this event a success. Give Nexon a little slack....
They can't just give an item away which was designed as a pay2win item, and they can't just lower the cost of the boxes to 1k per... Don't forget, it's extremely expensive for a gaming company to host a cross over event, and Nexon would need to make that money back somehow. Of course, a highly p2w item would be the first choice. That's pretty much how the game stays alive...
I think the best thing to do, to fix the issue with Reboot medal, would be to add this medal to an NPC for Mesos in Reboot world only. Even if the price was really high, it would be affordable to those who dedicate their time to progress in Reboot. It would also keep the non-p2w state of the Reboot server, and give players the chance to obtain an event-only item, making it fair for everyone.
I would suggest using a Luminous for FrankenBalrog Farming.
Luminous can spawn them at decent speed (Unsure if it's like this for all jobs, but i spawned 1 every 3 - 4 minutes in future Perion).
You can use Spectral Light skill to attack these monsters - Acts as standard attack, but with insanely fast attack speed compared to normal stabbing - Can also stand in 1 place, and use left/right arrow keys to move the skill around.
Can down a FrankenBalrog within 4 - 5 minutes.