I've been doing mobile a/c work for 35 years. To do the spider system right, you need at minimum:
new compressor [even chinese knockoff] $300
new dryer $100
new barrier hoses $150
r&r evaporator and condensor [if not leaky] flush completely--labor is huge to remove the evap
test and/or renew txv
leak check with nitrogen and trace amount of refrigerant
vacuum down system
recharge with r-12 [about 22 oz] a shop will upcharge this to at least $100
parts minimum $650.
I don't know any shops that will do this for $350 labor...i sure wouldn't
Now this doesn't include a conversion to 134a if the owner desires.
You are correct that the dryer needs to be installed last just before pulling a deep vacuum. It is also the easiest component to r&r.