One thing that most people have in abundance is cheap ballpoint pens that have advertisement on them. You can almost always get a ton of them at any kind of event. The issue with them is that you cant ever really be certain if they'll write good or not.
What I'd recommend is to buy a high quality pen and figure out a brand of ink refills that you like. The pen itself will last decades and the ink refills will guarantee a high level of writing quality. When it comes to picking ink refills, there are videos online to help you along.
I currently use a rotring 600 pen with parker style easyflow 9000 m refills.
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