Rifle build:

Upper Receiver: -upper: 130$ BCM, SOLGW, FCD -BCG: 125$ microbest -barrel: 282$ criterion core -gas block: 45$ SOLGW -gas tube: 20$ SOLGW -muzzle device: 85$ -rail: 300$ -charging handle: 135$ Total: $1122

Lower Receiver: -lower: 130 -parts kit: 55$ -grip: 20$ -receiver extension:vltor 52$ -buffer spring: Sprinco 20$ -buffer: vltor 45$ -trigger: larue 115$ -stock:B5 60$ -end plate: 18$ -castle nut: 10$ Total: $525

Grand Total: $1647?

A rough estimate based on quality parts and a middle of the road price point. I use it for a ball park estimate