My remap was £300, but it's normally £250 but my ECU had to be removed due to the security software not being cracked at the time.
Lowering yes, but not yet.
It's unlikely they would find it during regular servicing, it's not something they would look at. Even if they do look for one, the maps are hard to find although not impossible. Also you don't have to use stealers for your servicing
If SEAT release an ECU update they could flash it over and wipe the map, however most reputable mappers will put it back free or for a very small sum.
Hope this helps