Hello mate - pretty much all the ink writing I do is with a fountain pen - some are good - some are not - including many that - at a greater price - ought to be much better - drying out, or just pishing ink everywhere - for no readily apparent reason - within your stated budget - and from personal experience - I have used all of these models - and can recommend - the links are to a UK supplier - I have no idea where you are in the world - but you should be able to source them in most markets -
Pilot VPen (V4) Disposable Fountain Pen <i class="product-data" data-product-vat="20">£4.75</i> In stock now for fast UK and worldwide shipping.
www.cultpens.com
Bomb-proof - but are not refillable - for the cost - a superb nib. They will stay wet for weeks between uses.
Monami Olika Fountain Pen Fine <i class="product-data" data-product-vat="20">£3.49</i> In stock now for fast UK and worldwide shipping.
www.cultpens.com
For the price - a stand-out - takes standard international refills - or - surprisingly a converter - but I wouldn't bother with the latter option. A pig to clean between ink colour changes.
Zebra Disposable Fountain Pen <i class="product-data" data-product-vat="20">£2.25</i> In stock now for fast UK and worldwide shipping.
www.cultpens.com
In terms of the best writing experience of the pens I am highlighting - this would be my choice. Not refillable.
Platinum Preppy Fountain Pen Crystal <i class="product-data" data-product-vat="20">£4.99</i> In stock now for fast UK and worldwide shipping.
www.cultpens.com
My second choice of the above - refillable but, with propriety Platinum sized cartridges - not a problem really - as they are easily available and cheap - you can use international standard refills - but you'd need to get a converter cap - probably not worth the hassle.
Bear in mind - that all these pens are Japanese made - so - when they describe a medium nib - it means fine in European standards - extra fine - even more so - so - if your writing needs a broad line - you are going to have to stick another £5 or £10 on your budget - to get something suitable - ditto - stub, italic or flex nibs. Hope this helps - yours - I.
@Blademonkey