Choosing a pen is very important and practising with it during preparations is even more so. The most important thing about the pen is that it should be slim and lightweight. Halfway through your paper, your pen should not be the cause of fatigue and/or reduction in speed of writing. If possible, choose a soft tipped pen and not the 0.5mm sharp tipped ones. the latter ones tend to tear the papers when writing at speed. Also don’t forget to choose one with a rubber grip; the plastic of the pen will really start to hurt your index finger by the time you reach the last few questions.
Keeping these factors, and your requirement of reasonable price in mind, take a look at a few pens- Cello Pinpoint-XS, Cello Technotip, Cello Finegrip,Cello Gripper , Cello Maxriter F, Reynolds 045 Fine Carbure and Nataraj Classic Fine Ball Pen
All these pens are relatively lightweight but Cello Pinpoint and Cello Gripper aren’t so slim and do start to hurt the Proximal Interphalangeal joint of the thumb (talking from experience). This is only if you’re using a Tripod pen/pencil grasp.
List of Best pen for UPSC Mains exam
Cello Technotip is a slim pen but has a relatively sharp tip. If the answer sheet given to you in the exam is of an inferior quality, its sharp tip will probably tear through the pages.
Cello Finegrip is very slim, comes with a rubber grip and has a blunt tip. I prefer and use this pen. Cello Maxriter F is also a good choice because in spite of not being as slim as Finegrip, its slimmer around the part where you grip it. Maxriter’s refill also lasts longer than Finegrip!
Reynolds 045 Carbure and Nataraj Classic are slim and lightweight but the lack of lack of rubber grip will really start to hurt the index finger when after an hour or so.
My recommendation would be either Cello Finegrip or Cello Maxriter F. Whichever pen you decide on, please start using the pen during your preparations to get used to the grip and set a certain speed.