Custom Field fixed price add

[Bayron]

Hi, wanted to ask a question for a customfield.
The problem i'm trying to solve is that i need a custom field to add a fixed price, no matter quantity or other product specs.
It's a check the company offers and it's an additional price, but it multiplies it for quantity of the product, how can i avoid/modify this for this single customfield?
Or can i do it actually in other ways?
(It should be an option that may or may not be selected, at the selection adds a fixed price to the total that's it...pretty simple concept, but seems not the case with virtuemart  maybe it's just me)

EDIT:
Actually forgot to say i'm on Joomla 3.6.4 and Virtuemart 3.0.18

[AH]

Have you looked at this plugin

http://forum.virtuemart.net/index.php?topic=127362.0

[Bayron]

Yeah, saw that one, but in all the explanation didn't read anything about adding a static price that is not considered as "per unit";
Since looks like you created the plugin, do you think it is capable of doing this?

[Bayron]

I'll try to explain it better.

Product X costs 1€ per unit.
User adds to cart 100 units it's 100€.

Now, for uploaded images, the company either prints the image no matter what, or checks the img file/adjust it if it needs to.
If the customer wants the file to be checked etc.. the company charges 5€.

So 100 units with this feature would cost 105€.

With the actual custom fields it becomes 600€ 'couse it adds it in the "per unit price" so it becomes 6€*100 units.
How can i make it so it works as explained in the 105€ example?

[Milbo]

As extra product maybe? kind of bundle, so that they see the 100 prints and the check for the images as two articles

[AH]

Thanks for the additional information:-

You are correct -  The plugin does not do what you require

Max's solution seems the correct way

[Bayron]

Yeah, actually solved the problem like that. Seemed like the only way

[mohtashimj]

I am also getting same problem for my Virtuemart Store LIKE I have product price as $10 and custom field (for Set Up charges) created with price $50 and when user adding this products with quantity 10 then the products total price is calculating as $600 and which should calculate as $150 ($100 + $50) .
Please any one let me know if I can do that with the help of custom fields?