You have to remember you only had a quote, not a fixed price.
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I would see a quote as the final price in this instance, with the exception of possibly travel expenses.
any chargeable overrun should be brought to the customers attention before hand, possibly you don't have the money to pay?
there are little / no extra costs for the installer (just his time) its not a massive amount of time, its not like he paid a team to come over for 3 days costing him £5000.
If it was a builder id expect to have had a discussion half way thru the project explaining X y or Z needs doing and its going to cost £££ extra
However I would not have negotiated the camera prices, either I supply at my price, or you supply and if they go wrong or take ages to configure that's something you pay for / resolve