Isnt it about $75-$100 an amp, $60-$90 per set of speakers, $100-$150 if those 6.5" are components. They may not want to use your wire. You need fuses/or breakers, rca cables, distribution blocks, and they are gonna try and upsell sound deadening... Does your Head unit have inputs for 2 sets of rca cables? That might be a new head unit, or something else (on a 2018, I'm sure there are a lot of features you would like to keep which means not skimping out). In a perfect world, I would think $300-$500. If you have to do a bunch of other stuff mentioned, you're north of a thousand bucks. Then there's the real cost of an install; how much is it going to cost to fix it when they are done, and do it right. I've learned my lesson on shops. Here are SOME of the things I had to fix after a shop install..
They GLUED the tweeters from my component speakers into the door panel opening.
They cut the butt connectors off the tweeter wires so they could use caps.
They GLUED the bass knob on the dash.
They capped together three pieces of wires for my subwoofers for a 6ft length of wire.
They drilled screws through the back of the cab to mount the subwoofer boxes
They used two tiny self tapping screws, through the lug and not the lug hole to individually mount each amplifier (I have a problem thinking these self-tapping screws are big enough to ground well).
They didn't mount the amplifier or the distribution block
They mounted the crossovers in the door, (and now they have rust on the screw terminals).
They drilled holes through the cover of the crossover instead of taking 2 seconds to open them and using the mounting holes that are built in, (then covered the hole in the cover with electrical tape).
The Big 3 was them running one 1/0awg wire to the fender and didn't even clean off the paint, (they did 1 of 3).
GOOOOOOD LUCK!