availability

[gusto72]

Hi,
I'll try to explain my problem as clear as possible.
I'm trying to use prestashop for "selling" workshops. When you order, you have the options to just "buy" the workshop but also to order this with an option (an extra service). the option has an extra cost. I'm trying to do this by using the tab combinations in my product page. So far no problem, but...
The number of available places is for instance 6. Ofcourse I don't know in advance how many buyers are going to use the available option or are ordering without the option. But still I have to set my number of avalaible "stock" in each attribute. If I put 6 in each I could end up with 12 sales wich isn't OK. If I put 3 in each attribute and there are 4 or more buyers wanting to order with the extra option, they can't because I'm out of stock for that attribute.

Does this make any sense?

I really hope someone can help me out here, because without the possibility of setting a maximum "sales" on the "product" it is a showstopper for me...

thanks for any advice you might give

Gusto