if your not changing wheels you could probably skip the balance
usually your just doing seals, bush and thrust
intercooler will catch any chunks if you F up

450 in labour? at 100/hour sounds like a fair thing
you get a warranty too and support and advice dont begrudge what proffesionals charge for a proffesional job. it took them years to learn how to get it right

i want to have a go at mine one day but if it fails it will be on my own head
dazza