As soon as you start justifying your price it sounds like your making excuses IMO.
9 times out 10 the low bidder will do an perfectly good job, at least as far as the client is concerned.
I will negotiate on price, but there has to be something in it for me, ie leaving chips on site, paying cash, anything other than straight discounting.
I want to build a reputation for being on the expensive side, but 100% reliable. People will pay extra for peace of mind, especially through referrals. Iv been in my current location 5 years, still losing lots of work on price, but I am building a core of clients that are willing to pay extra to have me and recommend me to their friends.
So to answer your question, say nothing, your wasting your breath, save it for a client who cares.