So you are asking me (or, rather, asking me to ask the client) to:

1. Calculate the total cost of all the items in the kit
2. Calculate the difference between that cost and the intended cost of the kit as a whole
3. Divide that difference by the number of items in the kit
4. Adjust the price of each item, subtracting the divided difference
5. Do this all again should quantities or the price of the kit change…

…or maybe you're asking me (to ask the client) to simply…

1. Divide the intended kit cost by the number of items in the kit
2. Set the cost of each item to the divided value, regardless of what the item originally cost -- so the $400 embedded controller has the same price as the $3 bicycle reflector it's packaged with
3. Do this all again should quantities or the price of the kit change…

That's the problem… I can't really understand why this choice was made instead of just going with the single price, especially since this method seems to be much more difficult to implement programmatically.

The client is starting to get antsy and wanting to see their site up soon, but heck, maybe I have enough time to just hack together my own solution… I'll call it "Simple Kit" or something. I'd still like to hear from other store-builders, though -- maybe there's a simpler solution that I've overlooked.