Hi Jitendra
The best rated front/rear dash cam currently is Thinkware about £200 and recommended by Camera website Viofo A119 V3 - RECOMMENDED. Buy now from Amazon (£99.59)
There are always offerings by Nextbase who were one of the originals in the market
The price from your Independent seems really fair remember BMW do not make these they have them made badged and boxed so when you add the Dealers mark up and around £200 p/hour labour rate it isn't difficult to get to their price
Me I would DIY if that is beyond your skill set use the Independent
Dave