There are helmets costing ₹500, all the way to ₹25000. How much one should spend and what are the parameters to look for in a helmet to justify a higher price? 

Helmets are priced on these parameters:

1. Safety – The protection layers and the quality of protection layers a helmet comes with. For example, Mips based helmets are safer and in general cost more.
2. Comfort – Helmets can directly affect the comfort when cycling long distances. 
   • Weight and Ventilation are the 2 primary reasons. Expensive helmets are half the weight of a regular run of the mill ones. While it may seem light in your hands, the same when worn for a few hours feels heavy on the head and neck. A 100 gram saving on helmet weight is easily noticeable in a 2-3 hours ride btw.
   • Ventilation: Well ventilated helmets go a long way to keep the air flow going and  the head cool. The openings in the helmet are a good way to judge the potential ventilation. Some of the more performance (speed) oriented helmets don’t have ventilation but they are suited for short distance time trials only.
3. Aerodynamics – Aerodynamics matters more to riders who go on a fast road ride. Normally they already have an aero bike and deep section carbon wheels. Some helmets are designed specifically to cut through air better. Again they are primarily aimed at speed-enthusiasts and competitive cyclists. The gains are marginal but it is still there. Such helmets are positioned at premium buyers. 

Findbetter has a large collection of helmets from brands like Giro, Rudy Projects, MET, ABUS, Bell, Van Rysel & Indian brands like Zakpro, B+ve. Many of them are available with good discounts as well. Here are a few.

Giro Isode: https://findbetter.web.app/viewItemPageRoute?itemId=x20o2dbcvzxEFddaGtDO&sellerId=oCtZ6DFct2Y3aZuMQySaMc8kZBw1