Have you tried the Pilot 78G? It's a quite reliable and yet cheap fountain pen: https://www.penaddict.com/blog/2013/11/27/pilot-78g-fountain...
Are the 78Gs still manufactured, or have they been replaced with the Metropolitan? I haven't directly compared the 78G with Metropolitan, but I've been disappointed with how wide my Metro writes despite having a fine nib.
[1] https://www.jetpens.com/Pilot-Vpen-Disposable-Fountain-Pen-B...