you would need 4 items
flea market m4 with stock rails (~50k on flea)
the mechanic barter for mpx-sd (120k, but you will still keep
the mpx after)tx-15 upper (20k off flea)
supressor( i used the ultra 15(60k)) but you can try others
60 rounder
better charging handle/ ergo iron sights/ new handguard( basically easy ways to top up ergo)
first strip the m4 of its rear sight, stock pistol grip and muzzle device
then transfer the scope without the top reflex sight, shift handguard, omrg grip and mp7 stock over
mount the supressor, and see how much more ergo you need
ways to add ergo are
1.ergo irons
swap the handguard with the golden one(avoid mlok handguards since you cant buy 4.1in mounts)
better charging handle
better pistol grip
Source: https://www.reddit.com/r/EscapefromTarkov/comments/klmkhi/gunsmith_part_4_under_300k/