It makes sense. Thank you.
I know it's hard to explain this, but I DO want to add an increase of $20, if they select at least one out of the three attributes. And with that in mind, if they select all three attributes, I still want to have a total of $20.00 in the end (instead of 20 * 3 = 60).
Here is an example (non ZenCart):
http://www.mojotone.com/Narrow-Panel-Tweed-Champ-Style-Guitar-Amplifier-Combo-Speaker-Cabinet_3#.UUiwOhYo5hE
The cabinet is $194.38 if no Custom Cosmetics are selected. If even One (or all) custom attribute is selected (tolex, grille cloth or Handle) then the price jumps with $25.
It's not an orthodox way of doing things. Looks like they are using grouped attributes.
thanks for your patience to understand this.
gabi