They tell me another EC can do the job for $300.
I was figuring around $700.
They said they would pay me 400 because they knew me.
I have removed everything except the important parts of this post. See what's left is a customer trying to negotiate a better price.
Why would a customer offer you $400 to do a job that another licensed and hopefully competent EC would do for $300??? Would you give a mechanic an extra $100 just because you know him?
I really think that $300 quote is just wishfull thinking on the part of the customer (that's what they think the job is worth) and that's why they are willing to up the price to $400.
If you can and still make money try to negotiate it to $600 and skip all frills such as the spare circuit and use the cheapest materials possible.