I would definitely consider the TWSBI Eco fountain pen. They are reliable performers, feature an integrated piston filler, and are decently made for the $$. They have a wider section than the Pilot Metropolitan, and are also available as a "ECO-T" model which has the tripod grip section like the Lamy if desired. I own 3 TWSBI - and while the material is "slightly" less luxe feeling on an ECO than, say, a VAC 700R, it feels better than the Wing Sung pens I also have. Plus, better after-sale support if you buy from a retailer in your country (i.e., Goulet Pens in the US). ECO can be had for around $30. I own two, both in "stub" nibs, that I use mostly for calligraphy. My preference is for the Non-T ECO but then I have good "pen discipline" and don't roll them around. If you're prone to rolling the pen in your fingers,the ECO-T will help stabilize them in a proper tripod grip.
Main thing to consider is nib size and type. An ECO in EF (extra-fine) is about the same line/width as a Pilot Metropolitan F. However, in my hand, the ECO's EF nib (a German-sourced unit, from JoWo I think) is smoother and a better performer.
For $50, you can consider upgrading to a TWSBI 580. It's the "upgrade" version of the ECO, thought the ECO came later than the 5xx series. The 580 adds a swapable nib unit, metal fittings, and a faceted barrel for visual appeal/reduced rolling. It's not postable like the ECO is, so that may be a consideration.
At $70 is the VAC 700R series, which is the "ultimate" pen in their catalog. This features a VAC fill system, and even has a dedicated inkwell for use with it. However, I would avoid the 700R until you are more comfortable with filling systems as it's a bit more fiddly (you need to "unlock" the pen every time you use it more than a page or two).