All certified riding helmets go through the exact same testing and must pass that testing to be certified, period.
What makes a helmet more expensive is often the marketing, the sponsoring of popular professional riders and fad with fashion.
Yes, helmets can and do start at inexpensive prices and can easily go to near $1,000 dollars for a helmet off the shelf forget what a custom made costs.
From the Troxel brand "Sport" helmet starting at $29.74 to off the charts in expensive... https://www.statelinetack.com/Search...ding%20helmets
What is most important is a proper and comfortable fit so best protection is achieved as was mentioned.
A budget to about $75.00 will give you around 20 choices to try on and find one that fits and is liked.
There are many places to purchase a helmet from, but you truly need to go to a store and try on the make and model for the comfort factor and proper coverage with sizing.
Many stores will meet or beat a competitors price if given the chance...
The other added tidbit is every certified helmet inside has a date stamp...
That stamp is when the helmet was made, the closer the date to today's current date the best in technology and helmet manufacturers suggest replacing of helmets every 5 - 7 years from manufacturing date so you want a newer date not a helmet that has been sitting on the shelf collecting dust for 4 years.