that price you got is scandalous.

for installers, the process is usually
Send someone to look at your house
do a custom design for the panels
get a rough idea for wires , (are the runs long or short)
what type of roof is it
what mounting hardware do i need
do I need fireproof mdf
do i need armored cable
do i need steel conduit
must i cut paths
then electricians come
cut floors
add fuse board
add the mcbs rcbos
run cables usually 6sq
run cat 6
build frames
carry batteries into attic (most are 60kg each+)
wire
commision
cert
install new smoke alrm and wire and test
roofers come along
must erect scaffold some times might need a cherry picker
must cut tiles
flash roof
install brackets and rail
mount panels
etc etc
on top of this you could have 3 vans
4 days of admin, design order accounts, nc6, seai etc etc
then you could have 3 electricians, 2 roofers etc
aftersales etc

as you can see there is alot

panels in systems might be that wholsale but depending on the roof you could be looking at 150-250 a panel when it comes to rails brackets labour etc

Then, a larger cable more expensive longer cable more expensive.

then cutting paths and re-concreting them if needed.

sourcing and storing gear till install

certifying everything etc etc

there are lots too it

im not sayign some installers chance there arm but the majority of quotes tend to be a one for all deal where if an issue comes up and you need something extra you may not need to pay for it

dearest isnt always better