One of the finest and longest-lasting gadgets you can buy is a decent fountain pen. Like most items of good quality, maintenance and repair can keep them in action for years, if not decades: you can pay an expert, or you can learn to do it yourself.
Ludwig Tan’s how-to guide on grinding nibs saved me a bunch of cash getting an old Parker 51 writing smoothly again, and all you need is an Arkansas Stone, fine-grit emery paper and, finally, something only slightly rough, like crocus paper or a brown paper bag. As these are items you likely already have, it’s practically free!
There’s another article I wished I’d had at hand, though: Wim Geeraets’ Nib grinding experiences has more technical detail, such as the best grade papers to use as you proceed.
Update: As wisely indicated by commenters below, you should only do this with cheap nibs until you know what you’re doing.