What is the best cheap fountain pen?

The Platinum Preppy at around $7 is the honest answer: a genuinely good nib in a disposable-looking body, with a cap that seals well enough to leave inked for months. The Pilot Kakuno and Jinhao x159 make the same case in different shapes.

Under $25, the Pilot Metropolitan adds a brass body and a nib that embarrasses pens three times its price. Cheap in this hobby does not mean compromised — it means the margin went into the nib instead of the box.