New Post: Optional service to product purchase

Hello,
I have a case where together with the product a potential client should be able to purchase an optional installation (talking about physical installation of devices in a house, for instance).
Each product might have its own instalaltion fees.
I suppose one can do that by adding a model which includes the installation option, but in this case I already have several models and doubling that would be confusing and ugly.
[In my case, cost of installation varies by product and not by model.]

Using related products may not be suitable either.

Maybe it's obvious, but I do not see how I could do that. Any suggestion, please?

Thanks

Franco