at Excelcia we solved this in a rather ... unusual way.
we created some shiplights that look the same as the existing ones but they cost several M cash
works up to 10M per light.

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Excelcia Mod Leading Developer

Yeah, it's kind of funny to have people buy a Gunboat for 1Mil, but then have to pay 40 million for 4 running lights. =)

In order to do this, create a new entry in your light_equip.ini file with the same stats as an existing light, but just a new name, like:

[Light
nickname = DockingLightRedSmall10M
always_on = false
docking_light = true
bulb_size = 2
glow_size = 3
color = 255, 64, 64
flare_cone = 120, 90
min_color = 128, 32, 32
avg_delay = 0.500000
blink_duration = 0.500000

Then, open up your misc_good.ini file, and add in a new Good item for that light, with a price of 10Million, like this:

[Good
nickname = DockingLightRedSmall10M
equipment = DockingLightRedSmall10M
category = equipment
price = 9999999
combinable = false
material_library = equipment\models\li_equip.mat

Finally, open up your goods.ini file, and find the ship you want the change the price on. Change some of the lights to the new 10Million dollar lights (however many you want/can have on a ship) like this:

addon = DockingLightRedSmall10M, HpDockLight01, 1

Voila, you can now have prices for ships be more than 10Million =)

It's a good idea,
Thanks for your help.