I'm having issues with the company who will be supplying parts that i will be selling. They won't tell me the weight of the products that i'll be selling so my customers have to send me an email with all the things they want. I was wondering if i can have the checkout calculate the cost before shipping, email it to us, and ask the customer to wait for a reply with the total cost...

Also, if it's not possible with Zen Cart, which eCommerce thing will?

Thanks for your prompt response,
~Xander