I want a cheap daily driver pen

Suggest me really cheap pens with a good smooth nib that doesn't feel scratchy and ink that i can easily use on 70gsm paper without see-through.
I use rollerballs and gels that are very smooth writing and the nib size is 0.5 mm.
The reason I'm looking at fountain pens is that the refills for rollerballs is expensive and gel pens don't last my whole writing sessions.
I write anyhere from 30-45 pages A4 sheets per day, edge to edge.