Random unordered list of cheap fountain pens that I know to be halfway decent:

• The Zebra V-301. It has a (partially) metal body and is reasonably slim, and has a unique feed mechanism that allegedly prevents it from drying out even if unused for extended periods. Price: Approx. $5 US.
• The Pilot Penmanship. This is basically the refillable version of the Pilot Varsity and has a pretty similar nib. It takes Pilot’s usual wide neck cartridges. Plastic body, for some reason no pocket clip. It has a slightly elongated tapered body that’s maybe “quillish,” but not really. Price: Approx. $10 US.
• Pilot Parallel. This is a calligraphy pen with a flat/italic nib. This violates your maximum line width criteria even in its narrowest width (1.5mm) but definitely has an elongated dip pen/desk pen type of shape which may be what you like. Price: Approx $12 US.
• The Platinum Preppy. Everyone raves about these as the quintessential beginner’s fountain pen but I personally don’t see the appeal. Plastic body, flimsy clip, but writes pretty good. It’s cheap, though. Price: Approx. $6 US.
• The Platinum Desk Pen, suggested elsewhere in this thread. It also has an elongated dip pen style body. Price: Approx $13 US.
• Honorable mention: The Jinhao 85. This is a knockoff of the revived Parker '51, and has a similar hooded nib style. I own one and it looks sharp and writes well, too. Price: Approx. $15 USD.

The Lamy Joy, Safari, and Al-Star may also fit your needs but are likely outside your budget. Lamy pens have very easily interchangeable nibs so you’re not locked into whatever width you started with forever which is nice if you decide you’d like a broader or narrower point later and you won’t have to buy a whole new pen. The Joy is also a calligraphy pen but has that elongated dip pen/quill shape. You could kit it with a normal nib if you wanted; I think a Lamy Fine or Medium nib would meet your line width requirement.

If you really, really want to have the quill pen experience you can get a dip pen. These will require you to be tethered to an inkwell at all times. The Speedball nib holder sets are ubiquitous and very inexpensive, and can be had easily at most arts and crafts stores. A dizzying array of different nibs are available for these which are very easily changed and extremely cheap.

As the other commentator stated, you’re looking for a FP.

The things you’re describing can be easily found… but they usually cost a lot to have all of the qualities at once.

That is unless you can get your hands on chinese FPs where you live. I get mine ftom aliexpress.

Now from my own personal experience you can’t go wrong with either Jinhao X159 or Jinhao Dadao 9019.

You can get a fine nib which I think is the perfect balance between smoothness and crispness.

Another tip: if you find that the feeling of the nib is not to your liking, you can tune the nib. There are many excellent tutorials for this and you can do it at home without special equipment.

Since money is a problem, you’ll probaly have to substitute it with your time in getting exactly what you want.

What you’re describing definitely sounds like a fountain pen–specifically, an eyedropper (where the body acts as the ink reservoir), desk (long, gently sloping body coming to a point) pen–did it look something like this? https://cdn11.bigcommerce.com/s-5ko0zosub2/product_images/description/sheaffer/sh_deskpen_greymarble_2.jpg (Sorry, can’t get images to embed)

For your thinish line requirements with a non-scratchy nib, I’d suggest a European/American fine or Japanese medium nib size (Japanese brands tend to run thinner). Most pens you can buy have some sort of cartridge, as well as a converter that would allow you to use a bottle–you can also get a cheap blunt tipped syringe or pipet and refill washed cartridges with whatever ink you want. I use a hot glue gun to reseal mine for transport, and peel it off before reinserting the cartridge.

I would recommend going to a stationary store/office supply store and trying some out! If you give us a general geographic area we can try to recommend stores near you that cary pens you could try–in Europe I’ve found this much more common than the US. If in-person testing isn’t an option, I would tentatively suggest a pilot kakuno–they look like they cost ~11€ in Europe, and come with one cartridge of ink. They’re Japanese so I would recommend a medium if you want to avoid scratchy at all costs, or a fine if you have some tolerance for a bit of feedback and want a thinner line. Any of pilot’s converters should work, looks like they cost ~6-12€ depending on refill mechanism and capacity.

A kakuno or other budget pen won’t look as amazing, but in my experience write almost as well as pens costing 10x more, and honestly if it’s your first one you probably won’t be able to feel the nuance yet.

In addition to the other recommendations, you can also still buy quills!

E.g. https://cultpens.com/products/manuscript-art-of-writing-quill-pen-and-ink-gift-set

No idea if they are any good.

I solve #1 with some very fine grit whetstones. Any time I have a pen I like whose nib is just a bit too scratchy I use a 4000-grit ruby whetstone to shape it,then a 10,000-grit or better one to polish it. I’ve managed to rescue some nibs that were constantly shaving strand of paper off a writing surface.

@01189998819991197253 Think it’s going to be hard to hit ALL the points.

The cheapest fountain pens are probably Jinhao, but nib QC is all over the place. Pilot has the most reliable nib QC, but the price for a Kakuno may be slightly out of budget. Could also consider the Platinum preppy, but they have more feedback than Pilots.

Not sure on mm widths. Finding larger than an M nib for any of the above is difficult or nonexistent.

All accept cartridges & converters.