The extra options function is great, but could definitely use improvement. Currently, it doesn't take into account availability of 'extra,' and it is time consuming and unnecessarily complicated to updated pricing in bulk.
What would be ideal (similar to the kit functionality but not quite the same) is to be able to add a SKU or choice of SKUs as Extra Options, either/both as a radio or drop down. What would be even better is an option to calculate the price of the extra option from the price of the SKU itself, and to be able to show the availability of that SKU on the webstore.