L.A.
I like the direction you are going in..
I would totally want to purchase your "basket"..
Maybe consider doing it in a "Happy Birthday" Gift Bag, stuff it with colored tissue and place the gift cards on Dowels or crazy straws sticking out of the bag and tissue. Wrap this whole thing in clear Cellophane..
Make a big tag that explains the value of your custom Birthday Cake, the Value of the custom Invites and the amount the Party city Gift card (maybe add a dollar so it is an even $25... I bet it is almost if not more than $100. value..
When making up the gift cards for your cake and the invites.. Be VERY specific about quantities, how much time in advanced you need to be contacted to bake.. etc..
Also place a expiration date on it.. Like "1 year.. from purchase."
I guess you can tell I have chaired the Gift Basket Committee before, hee, hee..