The productoptions table is really just inventory. One row for each combination. I would probably not even use addprice, just make it productoptionprice, no math involved.
Can a single accessory be used with multiple products? Is a different accessory necessary for different product options? For example a red leg rest for a red wheel chair or whatever.
I think Ray is right in that accessories are just products and belong in the product table they just have a different producttype=accessory. You could go back to the productoptions table if you need to associate one accessory with several products.