Thank you in advance to anyone who chooses to answer this question....

I'm trying to select a shopping cart and I'm open to either a hosted solution or buying a cart. Cost is definitely an issue as we're doing this on somewhat of a shoestring and I anticipate low $$ sales volume for some time.

Very small start-up with small relatively low cost items and multiple configurations for each item; at least three drop down options per item including package size and packaging type which will both affect weight and price.

I have two primary concerns:

1. The ability to add product configuration options that will show the customer the price of the item after they select the size and product packaging. Almost all carts do this with varying degrees of front end user friendliness, a few carts I've demoed amazingly don't.

2. The ability to accurately calculate the shipping weight of multiple products that will be shipped in the same box. This one seems to be a doozy. I have yet to see a cart that will allow you to specify the shipping materials weight separately and spec max limits for how many of a product will fit in a specified shipping container/box size. I feel this is important because a significant number of our orders would fall within the 13oz limit USPS Parcel Post category which would save customers a ton of money on shipping. Is this impossible? I don't really understand how shipping rates are determined based on all the carts I've demoed so far. (x-cart was the only one that seemed to even come close to robust shipping options, but other things seemed less than stellar about it). I'm open to shipping functionality coming from a third party plug-in/extension if necessary. Impossible to evaluate any of these in a demo mode.

Some must haves:
Customer Registration
Product Reviews
Authorize.net as a payment gateway option
Decent SEO tools

If I haven't already ruled out every cart in existence I would also like to have:
Templates that don't look like dog poo
Discount Coupons
Wish List would be nice, can live without it