
Unlike the lists that Brad at Pen Addict does where pens are sorted into rollerball, fountain, etc., I’m grouping my Top Five lists by price point. Obviously, prices may vary slightly depending on your location but this is based on average US dollar prices.
This list is in no particular order, just the five best under-$5 pens in my opinion. The pen equivalents of “gateway drugs”.

The Budget Fountain Pen: Platinum Preppy Fountain Pen in F or EF
If you want to get in to fountain pens but don’t know where to start or even if you’ll enjoy them, this is a good place to start. While they are not the prettiest pens at the prom, for $5 or less, you can at least try out what its like to write with a fountain pen. They are pretty reliable although they can be a little scratchy. Did you hear me? They can be a little scratchy! So don’t base all fountain pens on these because they are $5 not $50. Over $25, I get guarantee you a smooth writing experience with a fountain pen but start here. See if you like the light touch needed to write with a fountain pen using a $5 pen before advancing to something more expensive. And once you graduate to a more expensive tool, you can use the Preppy to learn how to nib tune.
$3.95 for F, $4.98 for EF (via Goulet Pens)

The Gel Pen: Uni-ball Signo UM-151 Gel Ink Pen (0.28, 0.38 or 0.5). The UM-138 RT in 0.38mm, the RT1 and the UM-100 capped line are all equally good)
This is the measure for all other gel ink pens. This category is very competitive so its tough to pick THE BEST but the reliability and smoothness of the Signo line sets the bar pretty high. Most of these pens are easy to disassemble and use the refill in other pens since they are largely Pilot G2 compatible-sized.
$1.65 – $2.50 depending on model (via Jet Pens)
Runners up: Zebra Sarasa Clip, Pilot G2, and Pilot Juice. These are all excellent gel ink pens available in an array of colors and tip sizes. Whether you prefer a bold black line or a dainty sakura cherry blossom pink hairline, any of these options have got you covered.

The Rollerball: Pilot V5 Precise Rollerball This is the pen that introduced me to alternatives to a Bic Stic. Still a good option for a quick.
These retail for about $20/dozen or $10/5-pack. Available in seven colors, retractable or refills for retractable (looks like a G2 compatible refill but will verify). Since they are available in most US big box and office supply stores, this is a great gateway pen. Like the Pilot G-2, if you haven’t tried a pen not swiped from a pharmaceutical rep or your office supply cupboard, start here.
(Runner-up: The Morning Glory Mach 3 0.38mm. The Mach 3 is not as easy to find as a the Pilot V5 Precise but is as good or better and available in a wider variety of ink colors)

The Ballpoint: Uni-Ball Jetstream
Generally speaking, I avoid ballpoint pens. As a lefty, they smear, smudge and perform intermittently for me. So for me to recommend any ballpoint pen at all is fairly high praise. I recommend the Uni-Ball Jetstream to meet all your ball point pen needs. If you’re shopping in a office supply big box in the US, try the 0.7mm or smaller. If you’re willing to shop online, then I really like the 0.5mm available at Jet Pens in a variety of colors but my favorite is still the green grey model I bought in Hong Kong. Again, this is a pen that is widely available but I recommend the smaller tip sizes. The larger ones are often gloppy. The 0.5mm are really the sweet spot especially if you’re writing in a small book like a Field Notes or a planner.
Uni-Ball Jetstream pens are widely available in local shops and online in a variety of configurations starting at about $2.50.

The Felt Tip: The Sharpie Pen.
Honestly, a year ago, I would never have said this. I really like the Sharpie Pen. I thought I was a tried-and-true supporter of the Marvy Le Pen for my felt tip pen needs but I’ve embraced the Sharpie Pen as an excellent option in this category. While not as diverse in color options as the Le Pen, the Sharpie Pen is readily available in most US big box and office supply stores making them a good option in a hurry. I had a couple experiences with the Sharpie pen where is bled and feathered but I think it might have been a Moleskine book to blame and not the pen. Since then, I have come to appreciate the versatility and availability of the Sharpie Pen. Its more water resistant than Le Pen and the tip does not degrade as quickly.
Individual pens are sold from about $2 each and are available in blister packs and boxes in larger quantities and color options.