There are three classes of DSC (Digital Signature Certificate). For the purpose of GST, RoC, IT, Class II A type of DSC is sufficient. If you are involved in e-tendering, you need Class III DSC. Government of India has licensed a few organizations for providing the DSC services. Check out the article below for the list of organizations offering DSC:

https://gadgets.ndtv.com/internet/features/digital-signature-certificate-free-india-how-to-price-use-comparison-where-certifying-authorities-1856890

Further, eMudra and Certificate Digital

Also check out http://www.esolutions.net.in as you can not buy single certificate from certificate.digital.

For pricing, check this link: http://www.esolutions.net.in/price-list-digital-signature-certificates.html

are among the prominent service providers which are relatively cheap. What is surprising is the video/voice recording required by the government of india for DSC certificate which is probably not there in USA or UK.