Carlos This is confusing for our customers when we tried this when we first launched.
What we did is to put 0 in main item then in description "Starts @ 209"
Then put a variant of single select for sizes so they will be forced to pick one.
Small: 209
Mediaum 359
Large: 499
getmytrend the reason you are seeing 0 there is because your customization (small,medium,large) is supposed to be single select than multiple select.